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Gold

2025-05-21T04:31:47Z

Roger.Billings: Created page with "{{#seo: |description= Gold is a chemical element; its chemical symbol is Au and atomic number 79. In its pure form, it is a bright, slightly orange-yellow, dense, soft, malleable, }} {{about|the element}} {{redirect|Element 79|the anthology|Element 79 (anthology){{!}}''Element 79'' (anthology)}} {{pp-vandalism|small=yes}} {{pp-move}} {{Use dmy dates|date=March 2024}} {{infobox gold}} '''Gold''' is a chemical element; its chemical symbol is '''Au''' (from Latin {{lang|la..."

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|description= Gold is a chemical element; its chemical symbol is Au and atomic number 79. In its pure form, it is a bright, slightly orange-yellow, dense, soft, malleable,
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{{about|the element}}
{{redirect|Element 79|the anthology|Element 79 (anthology){{!}}''Element 79'' (anthology)}}
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{{Use dmy dates|date=March 2024}}
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'''Gold''' is a chemical element; its chemical symbol is '''Au''' (from Latin {{lang|la|aurum}}) and atomic number 79. In its pure form, it is a bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal, a group 11 element, and one of the noble metals. It is one of the least reactive chemical elements, being the second-lowest in the reactivity series. It is solid under standard conditions.

Gold often occurs in free elemental (native state), as nuggets or grains, in rocks, veins, and alluvial deposits. It occurs in a solid solution series with the native element silver (as in electrum), naturally alloyed with other metals like copper and palladium, and mineral inclusions such as within pyrite. Less commonly, it occurs in minerals as gold compounds, often with tellurium (gold tellurides).

Gold is resistant to most acids, though it does dissolve in aqua regia (a mixture of nitric acid and hydrochloric acid), forming a soluble tetrachloroaurate anion. Gold is insoluble in nitric acid alone, which dissolves silver and base metals, a property long used to refine gold and confirm the presence of gold in metallic substances, giving rise to the term 'acid test'. Gold dissolves in alkaline solutions of cyanide, which are used in mining and electroplating. Gold also dissolves in mercury, forming amalgam alloys, and as the gold acts simply as a solute, this is not a chemical reaction.

A relatively rare element,<ref>{{cite book |last=Duckenfield |first=Mark |publisher=Routledge |date=2016 |title=The Monetary History of Gold: A Documentary History, 1660–1999 |url=https://books.google.com/books?id=VeJmDAAAQBAJ&pg=PA4 |page=4 |quote=Its scarcity makes it a useful store of value; however, its relative rarity reduced its utility as a currency, especially for transactions in small denominations. |isbn=978-1-315-47612-4}}</ref><ref>{{cite book |last=Pearce |first=Susan M. |publisher=Smithsonian Books |date=1993 |title=Museums, Objects, and Collections: A Cultural Study |url=https://books.google.com/books?id=M6aZBwAAQBAJ&pg=PT53 |page=53 |quote=Its scarcity makes it a useful store of value; however, its relative rarity reduced its utility as a currency, especially for transactions in small denominations. ... Rarity is, nevertheless, in itself a source of value, and so is the degree of difficulty which surrounds the winning of the raw material, especially if it is exotic and has to be brought some distance. Gold is, geologically, a relatively rare material on Earth and occurs only in specific places which are remote from most other places. |isbn=978-1-58834-517-2}}</ref> gold is a precious metal that has been used for coinage, jewelry, and other works of art throughout recorded history. In the past, a gold standard was often implemented as a monetary policy. Gold coins ceased to be minted as a circulating currency in the 1930s, and the world gold standard was abandoned for a fiat currency system after the Nixon shock measures of 1971.

In 2023, the world's largest gold producer was China, followed by Russia and Australia.<ref name="Gold Production-2023">{{cite web |title=Gold Production & Mining Data by Country |date=7 June 2023 |url=https://www.gold.org/goldhub/data/gold-production-by-country}}</ref> {{as of|2020}}, a total of around 201,296 tonnes of gold exist above ground.<ref>{{cite web |title=Above-ground stocks |url=https://www.gold.org/goldhub/data/above-ground-stocks |publisher=gold.org |access-date=18 October 2021}}</ref> If all of this gold were put together into a cube shape, each of its sides would measure {{convert|21.7|m|ft|sp=us}}. The world's consumption of new gold produced is about 50% in jewelry, 40% in investments, and 10% in industry.<ref name="Soos-2011">{{cite news |last=Soos |first=Andy |title=Gold Mining Boom Increasing Mercury Pollution Risk |date=6 January 2011 |publisher=Oilprice.com |url=http://oilprice.com/Metals/Gold/Gold-Mining-Boom-Increasing-Mercury-Pollution-Risk.html |work=Advanced Media Solutions, Inc. |access-date=26 March 2011}}</ref> Gold's high malleability, ductility, resistance to corrosion and most other chemical reactions, as well as conductivity of electricity have led to its continued use in corrosion-resistant electrical connectors in all types of computerized devices (its chief industrial use). Gold is also used in infrared shielding, the production of colored glass, gold leafing, and tooth restoration. Certain gold salts are still used as anti-inflammatory agents in medicine.

== Characteristics ==
[[File:Au atomic wire.jpg|thumb|left|Gold can be drawn into a monatomic wire, and then stretched more before it breaks.<ref name="Kizuka-2008" />]]
[[File:Small gold nugget 5mm dia and corresponding foil surface of half sq meter.jpg|thumb|left|A gold nugget of {{convert|5|mm|abbr=on}} in size can be hammered into a gold foil of about {{convert|0.5|m2|abbr=on}} in area.]]
Gold is the most malleable of all metals. It can be drawn into a wire of single-atom width, and then stretched considerably before it breaks.<ref name="Kizuka-2008">{{cite journal |last=Kizuka |first=Tokushi |title=Atomic configuration and mechanical and electrical properties of stable gold wires of single-atom width |url=https://tsukuba.repo.nii.ac.jp/record/16027/files/PRB-77_15.pdf |archive-url=https://web.archive.org/web/20210716175414/https://tsukuba.repo.nii.ac.jp/record/16027/files/PRB-77_15.pdf |archive-date=16 July 2021 |url-status=live |journal=Physical Review B |volume=77 |issue=15 |pages=155401 |date=1 April 2008 |bibcode=2008PhRvB..77o5401K|issn=1098-0121 |doi=10.1103/PhysRevB.77.155401 |hdl-access=free |hdl=2241/99261}}</ref> Such nanowires distort via the formation, reorientation, and migration of dislocations and crystal twins without noticeable hardening.<ref>{{cite journal |last1=Che Lah |first1=Nurul Akmal |last2=Trigueros |first2=Sonia |title=Synthesis and modelling of the mechanical properties of Ag, Au and Cu nanowires |journal=Science and Technology of Advanced Materials |volume=20 |issue=1 |pages=225–261 |year=2019 |bibcode=2019STAdM..20..225L |pmid=30956731 |pmc=6442207 |doi=10.1080/14686996.2019.1585145|issn = 1468-6996 }}</ref> A single gram of gold can be beaten into a sheet of {{convert|1|m2}}, and an avoirdupois ounce into {{convert|300|sqft|disp=flip}}. Gold leaf can be beaten thin enough to become semi-transparent. The transmitted light appears greenish-blue because gold strongly reflects yellow and red.<ref>{{cite web |url=http://www.webexhibits.org/causesofcolor/9.html |title=Gold: causes of color |access-date=6 June 2009}}</ref> Such semi-transparent sheets also strongly reflect infrared light, making them useful as infrared (radiant heat) shields in the visors of heat-resistant suits and in sun visors for spacesuits.<ref>{{cite book |title=Suiting up for space: the evolution of the space suit |last=Mallan |first=Lloyd |date=1971 |publisher=John Day Co. |isbn=978-0-381-98150-1 |page=216}}</ref> Gold is a good conductor of heat and electricity.

Gold has a density of 19.3 g/cm3, almost identical to that of tungsten at 19.25 g/cm3; as such, tungsten has been used in the counterfeiting of gold bars, such as by plating a tungsten bar with gold.<ref name="Gray-2008">{{cite magazine |last=Gray |first=Theo |title=How to Make Convincing Fake-Gold Bars |url=http://www.popsci.com/diy/article/2008-03/how-make-convincing-fake-gold-bars |magazine=Popular Science |date=14 March 2008 |access-date=18 June 2008}}</ref><ref>Willie, Jim (18 November 2009) "[http://www.kitco.com/ind/willie/nov182009.html Zinc Dimes, Tungsten Gold & Lost Respect] {{webarchive |url=https://web.archive.org/web/20111008050729/http://www.kitco.com/ind/willie/nov182009.html |date=8 October 2011}}". Kitco</ref><ref>{{cite web |url=http://news.coinupdate.com/largest-private-refinery-discovers-gold-plated-tungsten-bar-0171/ |title=Largest Private Refinery Discovers Gold-Plated Tungsten Bar | Coin Update |website=news.coinupdate.com}}</ref><ref>{{cite news |title=Austrians Seize False Gold Tied to London Bullion Theft |work=The New York Times |access-date=25 March 2012 |date=22 December 1983 |url=https://www.nytimes.com/1983/12/22/world/austrians-seize-false-gold-tied-to-london-bullion-theft.html}}</ref> By comparison, the density of lead is 11.34 g/cm3, and that of the densest element, osmium, is {{val|22.588|0.015|u=g/cm3}}.<ref name="Arblaster-1995">{{cite journal |last=Arblaster |first=J. W. |title=Osmium, the Densest Metal Known |journal=Platinum Metals Review |volume=39 |issue=4 |date=1995 |page=164 |doi=10.1595/003214095X394164164 |s2cid=267393021 |url=http://www.technology.matthey.com/pdf/pmr-v39-i4-164-164.pdf |access-date=14 October 2016 |archive-date=18 October 2016 |archive-url=https://web.archive.org/web/20161018195547/http://www.technology.matthey.com/pdf/pmr-v39-i4-164-164.pdf |url-status=dead }}</ref>

=== Color ===
{{Main|Colored gold}}
[[File:Gold bullion ap 001.JPG|thumb|Gold bars, also called ingots or bullion]]
[[File:Ag-Au-Cu-colours-english.svg|thumb|left|Different colors of Ag–Au–Cu alloys]]
Whereas most metals are gray or silvery white, gold is slightly reddish-yellow.<ref name="Lippincott-1880">{{cite book |title=Encyclopædia of Chemistry, Theoretical, Practical, and Analytical, as Applied to the Arts and Manufacturers: Glass-zinc |url=https://books.google.com/books?id=o-FYAAAAYAAJ&pg=PA70 |year=1880 |publisher=J.B. Lippincott & Company |pages=70–}}</ref> This color is determined by the frequency of plasma oscillations among the metal's valence electrons, in the ultraviolet range for most metals but in the visible range for gold due to relativistic effects affecting the orbitals around gold atoms.<ref>{{cite web |url=http://math.ucr.edu/home/baez/physics/Relativity/SR/gold_color.html |title=Relativity in Chemistry |publisher=Math.ucr.edu |access-date=5 April 2009}}</ref><ref>{{Cite journal |first1=Hubert |last1=Schmidbaur |first2=Stephanie |last2=Cronje |first3=Bratislav |last3=Djordjevic |first4=Oliver |last4=Schuster |journal=Chemical Physics |volume=311 |pages=151–161 |title=Understanding gold chemistry through relativity |doi=10.1016/j.chemphys.2004.09.023 |date=2005 |issue=1–2 |bibcode=2005CP....311..151S}}</ref> Similar effects impart a golden hue to metallic caesium.

Common colored gold alloys include the distinctive eighteen-karat rose gold created by the addition of copper. Alloys containing palladium or nickel are also important in commercial jewelry as these produce white gold alloys. Fourteen-karat gold-copper alloy is nearly identical in color to certain bronze alloys, and both may be used to produce police and other badges. Fourteen- and eighteen-karat gold alloys with silver alone appear greenish-yellow and are referred to as green gold. Blue gold can be made by alloying with iron, and purple gold can be made by alloying with aluminium. Less commonly, addition of manganese, indium, and other elements can produce more unusual colors of gold for various applications.<ref name="WorldGoldCouncil" />

Colloidal gold, used by electron-microscopists, is red if the particles are small; larger particles of colloidal gold are blue.<ref>{{Cite book |url=https://books.google.com/books?id=MzT9eWxtmRgC&pg=PA180 |title=Electron Microscopy in Microbiology |date=1988 |publisher=Academic Press |isbn=978-0-08-086049-7}}</ref>

=== Isotopes ===
{{Main|Isotopes of gold}}
Gold has only one stable isotope, {{chem|197|Au}}, which is also its only naturally occurring isotope, so gold is both a mononuclidic and monoisotopic element. Thirty-six radioisotopes have been synthesized, ranging in atomic mass from 169 to 205. The most stable of these is {{chem|195|Au}} with a half-life of 186.1 days. The least stable is {{chem|171|Au}}, which decays by proton emission with a half-life of 30 μs. Most of gold's radioisotopes with atomic masses below 197 decay by some combination of proton emission, α decay, and β+ decay. The exceptions are {{chem|195|Au}}, which decays by electron capture, and {{chem|196|Au}}, which decays most often by electron capture (93%) with a minor β− decay path (7%).<ref>{{cite web |url=http://www.nndc.bnl.gov/nudat2/ |website=National Nuclear Data Center |title=Nudat 2 |access-date=12 April 2012}}</ref> All of gold's radioisotopes with atomic masses above 197 decay by β− decay.<ref name="Audi-2003">{{NUBASE 2003}}</ref>

At least 32 nuclear isomers have also been characterized, ranging in atomic mass from 170 to 200. Within that range, only {{chem|178|Au}}, {{chem|180|Au}}, {{chem|181|Au}}, {{chem|182|Au}}, and {{chem|188|Au}} do not have isomers. Gold's most stable isomer is {{chem|198m2|Au}} with a half-life of 2.27 days. Gold's least stable isomer is {{chem|177m2|Au}} with a half-life of only 7 ns. {{chem|184m1|Au}} has three decay paths: β+ decay, isomeric transition, and alpha decay. No other isomer or isotope of gold has three decay paths.<ref name="Audi-2003" />

==== Synthesis ====
{{See also|Synthesis of precious metals}}
The possible production of gold from a more common element, such as lead, has long been a subject of human inquiry, and the ancient and medieval discipline of alchemy often focused on it; however, the transmutation of the chemical elements did not become possible until the understanding of nuclear physics in the 20th century. The first synthesis of gold was conducted by Japanese physicist Hantaro Nagaoka, who synthesized gold from mercury in 1924 by neutron bombardment.<ref>{{Cite journal |last1=Miethe |first1=A. |title=Der Zerfall des Quecksilberatoms |doi=10.1007/BF01505547 |journal=Die Naturwissenschaften |volume=12 |issue=29 |pages=597–598 |year=1924 |bibcode=1924NW.....12..597M|s2cid=35613814 }}</ref> An American team, working without knowledge of Nagaoka's prior study, conducted the same experiment in 1941, achieving the same result and showing that the isotopes of gold produced by it were all radioactive.<ref>{{cite journal |last1=Sherr |first1=R. |first2=K. T. |last2=Bainbridge |first3=H. H. |last3=Anderson |name-list-style=amp |title=Transmutation of Mercury by Fast Neutrons |date=1941 |journal=Physical Review |volume=60 |issue=7 |pages=473–479 |doi=10.1103/PhysRev.60.473 |bibcode=1941PhRv...60..473S}}</ref> In 1980, Glenn Seaborg transmuted several thousand atoms of bismuth into gold at the Lawrence Berkeley Laboratory.<ref>{{Cite journal|last1=Aleklett |first1=K.|last2=Morrissey |first2=D.|last3=Loveland |first3=W.|last4=McGaughey |first4=P.|last5=Seaborg |first5=G.|year=1981|title=Energy dependence of 209Bi fragmentation in relativistic nuclear collisions|journal=Physical Review C|volume=23 |issue=3 |page=1044|bibcode=1981PhRvC..23.1044A|doi=10.1103/PhysRevC.23.1044}}</ref><ref>{{cite news |url=https://www.telegraph.co.uk/education/4791069/The-Philosophers-Stone.html |newspaper=The Daily Telegraph |first=Robert |last=Matthews |title=The Philosopher's Stone |date=2 December 2001 |access-date=22 September 2020 }}</ref> Gold can be manufactured in a nuclear reactor, but doing so is highly impractical and would cost far more than the value of the gold that is produced.<ref>{{cite book |last1=Shipman |first1=James |last2=Wilson |first2=Jerry D. |last3=Higgins |first3=Charles A. |title=An Introduction to Physical Science |date=2012 |publisher=Cengage Learning |isbn=978-1-133-70949-7 |page=273 |edition=13th}}</ref>

== Chemistry ==
{{Main|Gold compounds}}
[[File:Gold(III) chloride solution.jpg|thumb|right|Gold(III) chloride solution in water]]
Although gold is the most noble of the noble metals,<ref>{{cite journal |doi=10.1038/376238a0 |title=Why gold is the noblest of all the metals |date=1995 |last1=Hammer |first1=B. |last2=Norskov |first2=J. K. |journal=Nature |volume=376 |issue=6537 |pages=238–240 |bibcode=1995Natur.376..238H|s2cid=4334587 }}</ref><ref>{{cite journal |doi=10.1103/PhysRevB.6.4370 |title=Optical Constants of the Noble Metals |date=1972 |last1=Johnson |first1=P. B. |last2=Christy |first2=R. W. |journal=Physical Review B |volume=6 |issue=12 |pages=4370–4379 |bibcode=1972PhRvB...6.4370J}}</ref> it still forms many diverse compounds. The oxidation state of gold in its compounds ranges from −1 to +5, but Au(I) and Au(III) dominate its chemistry. Au(I), referred to as the aurous ion, is the most common oxidation state with soft ligands such as thioethers, thiolates, and organophosphines. Au(I) compounds are typically linear. A good example is {{chem2|Au(CN)2(−)}}, which is the soluble form of gold encountered in mining. The binary gold halides, such as AuCl, form zigzag polymeric chains, again featuring linear coordination at Au. Most drugs based on gold are Au(I) derivatives.<ref>{{cite journal |last=Shaw III |first=C. F. |title=Gold-Based Medicinal Agents |journal=Chemical Reviews |date=1999 |volume=99 |issue=9 |pages=2589–2600 |doi=10.1021/cr980431o |pmid=11749494}}</ref>

Au(III) (referred to as auric) is a common oxidation state, and is illustrated by gold(III) chloride, {{chem2|Au2Cl6}}. The gold atom centers in Au(III) complexes, like other d8 compounds, are typically square planar, with chemical bonds that have both covalent and ionic character. Gold(I,III) chloride is also known, an example of a mixed-valence complex.

Gold does not react with oxygen at any temperature<ref>{{cite web |url=http://chemwiki.ucdavis.edu/Core/Inorganic_Chemistry/Descriptive_Chemistry/Elements_Organized_by_Block/2_p-Block_Elements/Group_16%253A_The_Oxygen_Family/Chemistry_of_Oxygen |title=Chemistry of Oxygen |website=Chemwiki UC Davis |access-date=1 May 2016 |date=2 October 2013 |archive-date=14 July 2016 |archive-url=https://web.archive.org/web/20160714004304/http://chemwiki.ucdavis.edu/Core/Inorganic_Chemistry/Descriptive_Chemistry/Elements_Organized_by_Block/2_p-Block_Elements/Group_16:_The_Oxygen_Family/Chemistry_of_Oxygen |url-status=dead }}</ref> and, up to 100 °C, is resistant to attack from ozone:<ref>{{cite book |editor-last1=Craig |editor-first1=B. D.|editor-last2= Anderson|editor-first2=D. B. |title=Handbook of Corrosion Data |date=1995 |publisher=ASM International |location=Materials Park, Ohio |isbn=978-0-87170-518-1 |page=587}}</ref>
<math chem display=block>\ce{Au + O2 -> }(\text{no reaction})</math>
<math chem display=block>\ce{Au{} + O3 ->[{}\atop{t<100^\circ\text{C}}] }(\text{no reaction})</math>

Some free halogens react to form the corresponding gold halides.<ref>{{Cite book |last1=Wiberg |first1=Egon |last2=Wiberg |first2=Nils |last3=Holleman |first3=Arnold Frederick |name-list-style=amp |date=2001 |title=Inorganic Chemistry |edition=101st |publisher=Academic Press |isbn=978-0-12-352651-9 |page=1286 }}</ref> Gold is strongly attacked by fluorine at dull-red heat<ref>{{Cite book |url=https://books.google.com/books?id=Mtth5g59dEIC |title=Inorganic Chemistry |last1=Wiberg |first1=Egon |last2=Wiberg |first2=Nils |date=2001 |publisher=Academic Press |isbn=978-0-12-352651-9 |page=404}}</ref> to form gold(III) fluoride {{chem2|AuF3}}. Powdered gold reacts with chlorine at 180 °C to form gold(III) chloride {{chem2|AuCl3}}.<ref>{{harvnb|Wiberg|Wiberg|Holleman|2001|pp=1286–1287}}</ref> Gold reacts with bromine at 140 °C to form a combination of gold(III) bromide {{chem2|AuBr3}} and gold(I) bromide AuBr, but reacts very slowly with iodine to form gold(I) iodide AuI:
<chem display=block>2 Au{} + 3 F2 ->[{}\atop\Delta] 2 AuF3</chem>
<chem display=block>2 Au{} + 3 Cl2 ->[{}\atop\Delta] 2 AuCl3</chem>
<chem display=block>2 Au{} + 2 Br2 ->[{}\atop\Delta] AuBr3{} + AuBr</chem>
<chem display=block>2 Au{} + I2 ->[{}\atop\Delta] 2 AuI</chem>

Gold does not react with sulfur directly,<ref name="Emery-1961">{{cite web |url=http://library.lanl.gov/cgi-bin/getfile?rc000062.pdf |last1=Emery |first1=J. F. |last2=Ledditcotte |first2=G. W. |title=Nuclear Science Series (NAS-NS 3036) The Radio Chemistry of Gold |date=May 1961 |agency=US Atomic Energy Commission |publisher=National Academy of Sciences — National Research Council — Subcommittee on Radio Chemistry |location=Oak Ridge, TN |url-status=live |access-date=24 February 2021 |archive-url=https://web.archive.org/web/20041110193206/http://library.lanl.gov/cgi-bin/getfile?rc000062.pdf |archive-date=10 November 2004}}</ref> but gold(III) sulfide can be made by passing hydrogen sulfide through a dilute solution of gold(III) chloride or chlorauric acid.

Unlike sulfur, phosphorus reacts directly with gold at elevated temperatures to produce gold phosphide (Au2P3).<ref>{{cite journal |author1=Wolfgang Jeitschko |author2=Manfred H. Moller |title=The crystal structures of Au2P3 and Au7P10I, polyphosphides with weak Au–Au interactions |journal=Acta Crystallographica B |date=1979 |volume=35 |issue=3 |pages=573–579 |doi=10.1107/S0567740879004180 |bibcode=1979AcCrB..35..573J |language=en}}</ref>

Gold readily dissolves in mercury at room temperature to form an amalgam, and forms alloys with many other metals at higher temperatures. These alloys can be produced to modify the hardness and other metallurgical properties, to control melting point or to create exotic colors.<ref name="WorldGoldCouncil" />

Gold is unaffected by most acids. It does not react with hydrofluoric, hydrochloric, hydrobromic, hydriodic, sulfuric, or nitric acid. It does react with selenic acid, and is dissolved by aqua regia, a 1:3 mixture of nitric acid and hydrochloric acid. Nitric acid oxidizes the metal to +3 ions, but only in minute amounts, typically undetectable in the pure acid because of the chemical equilibrium of the reaction. However, the ions are removed from the equilibrium by hydrochloric acid, forming {{chem2|AuCl4(−)}} ions, or chloroauric acid, thereby enabling further oxidation:
<chem display=block>2 Au{} + 6 H2SeO4 ->[{}\atop{200^\circ\text{C}}] Au2(SeO4)3{} + 3 H2SeO3{} + 3 H2O</chem>
<chem display=block>Au{} + 4HCl{} + HNO3 -> HAuCl4{} + NO\uparrow + 2H2O </chem>

Gold is similarly unaffected by most bases. It does not react with aqueous, solid, or molten sodium or potassium hydroxide. It does however, react with sodium or potassium cyanide under alkaline conditions when oxygen is present to form soluble complexes.<ref name="Emery-1961" />

Common oxidation states of gold include +1 (gold(I) or aurous compounds) and +3 (gold(III) or auric compounds). Gold ions in solution are readily reduced and precipitated as metal by adding any other metal as the reducing agent. The added metal is oxidized and dissolves, allowing the gold to be displaced from solution and be recovered as a solid precipitate.

=== Rare oxidation states ===
Less common oxidation states of gold include −1, +2, and +5.

The −1 oxidation state occurs in aurides, compounds containing the {{chem2|Au−}} anion. Caesium auride (CsAu), for example, crystallizes in the caesium chloride motif;<ref name="Jansen-2005">{{Cite journal |title=Effects of relativistic motion of electrons on the chemistry of gold and platinum |first=Martin |last=Jansen |journal=Solid State Sciences |volume=7 |issue=12 |date=2005 |doi=10.1016/j.solidstatesciences.2005.06.015 |pages=1464–1474 |bibcode=2005SSSci...7.1464J|doi-access=free}}</ref> rubidium, potassium, and tetramethylammonium aurides are also known.<ref name="Holleman-2001">{{cite book |last1=Holleman |first1=A. F. |last2=Wiberg |first2=E. |title=Inorganic Chemistry |publisher=Academic Press |location=San Diego |year=2001 |isbn=978-0-12-352651-9}}</ref> Gold has the highest electron affinity of any metal, at 222.8 kJ/mol, making {{chem2|Au−}} a stable species,<ref name="Jansen-2008">{{cite journal |last=Jansen |first=Martin |title=The chemistry of gold as an anion |journal=Chemical Society Reviews |date=2008 |volume=37 |issue=9 |pages=1826–1835 |doi=10.1039/b708844m |pmid=18762832}}</ref> analogous to the halides.

Gold also has a –1 oxidation state in covalent complexes with the group 4 transition metals, such as in titanium tetraauride and the analogous zirconium and hafnium compounds. These chemicals are expected to form gold-bridged dimers in a manner similar to titanium(IV) hydride.<ref>{{cite journal |title= Gold Behaves as Hydrogen in the Intermolecular Self-Interaction of Metal Aurides MAu4 (M=Ti, Zr, and Hf) |first1= Jaehoon |last1= Jung |first2= Hyemi |last2= Kim |first3= Jong Chan |last3= Kim |first4= Min Hee |last4= Park |first5= Young-Kyu |last5= Han |journal= Chemistry: An Asian Journal |volume= 6 |issue= 3 |year= 2011 |pages= 868–872 |doi= 10.1002/asia.201000742 |pmid= 21225974 }}</ref>

Gold(II) compounds are usually diamagnetic with Au–Au bonds such as [{{chem2|Au(CH2)2P(C6H5)2]2Cl2}}. The evaporation of a solution of {{chem2|Au(OH)3}} in concentrated {{chem2|H2SO4}} produces red crystals of gold(II) sulfate, {{chem2|Au2(SO4)2}}. Originally thought to be a mixed-valence compound, it has been shown to contain {{chem2|Au2(4+)}} cations, analogous to the better-known mercury(I) ion, {{chem2|Hg2(2+)}}.<ref>{{Cite journal |last=Wickleder |first=Mathias S. |doi=10.1002/1521-3749(200109)627:9<2112::AID-ZAAC2112>3.0.CO;2-2 |date=2001 |title=AuSO4: A True Gold(II) Sulfate with an Au24+ Ion |journal=Journal of Inorganic and General Chemistry |volume=627 |pages=2112–2114 |issue=9}}</ref><ref>{{Cite book |last=Wickleder |first=Mathias S. |title=Handbook of chalcogen chemistry: new perspectives in sulfur, selenium and tellurium |editor-first=Francesco A. |editor-last=Devillanova |publisher=Royal Society of Chemistry |date=2007 |isbn=978-0-85404-366-8 |pages=359–361 |url=https://books.google.com/books?id=IvGnUAaSqOsC&pg=PA359}}</ref> A gold(II) complex, the tetraxenonogold(II) cation, which contains xenon as a ligand, occurs in {{chem2|[AuXe4](Sb2F11)2}}.<ref>{{Cite journal |last1=Seidel |first1=S. |last2=Seppelt |first2=K. |title=Xenon as a Complex Ligand: The Tetra Xenono Gold(II) Cation in AuXe42+(Sb2F11−)2 |journal=Science |date=2000 |volume=290 |issue=5489 |pages=117–118 |doi=10.1126/science.290.5489.117 |pmid=11021792 |bibcode=2000Sci...290..117S}}</ref> In September 2023, a novel type of metal-halide perovskite material consisting of Au3+ and Au2+ cations in its crystal structure has been found.<ref>{{Cite web |last=University |first=Stanford |title=Striking rare gold: Researchers unveil new material infused with gold in an exotic chemical state |url=https://phys.org/news/2023-09-rare-gold-unveil-material-infused.html |access-date=2 October 2023 |website=phys.org |language=en}}</ref> It has been shown to be unexpectedly stable at normal conditions.

Gold pentafluoride, along with its derivative anion, {{chem2|AuF6-}}, and its difluorine complex, gold heptafluoride, is the sole example of gold(V), the highest verified oxidation state.<ref>{{Cite journal |last1=Riedel |first1=S. |last2=Kaupp |first2=M. |title=Revising the Highest Oxidation States of the 5d Elements: The Case of Iridium(+VII) |journal=Angewandte Chemie International Edition |date=2006 |volume=45 |issue=22 |pmid=16639770 |pages=3708–3711 |doi=10.1002/anie.200600274}}</ref>

Some gold compounds exhibit ''aurophilic bonding'', which describes the tendency of gold ions to interact at distances that are too long to be a conventional Au–Au bond but shorter than van der Waals bonding. The interaction is estimated to be comparable in strength to that of a hydrogen bond.

Well-defined cluster compounds are numerous.<ref name="Holleman-2001" /> In some cases, gold has a fractional oxidation state. A representative example is the octahedral species {{chem2|{Au(P(C6H5)3)}6(2+)}}.

== Origin ==
=== Gold production in the universe ===
[[File:Vredefort crater cross section 2.png|thumb|upright=1.8|Schematic of a NE (left) to SW (right) cross-section through the 2.020-billion-year-old Vredefort impact structure in South Africa and how it distorted the contemporary geological structures. The present erosion level is shown. Johannesburg is located where the Witwatersrand Basin (the yellow layer) is exposed at the "present surface" line, just inside the crater rim, on the left. Not to scale.]]

Gold in the universe is produced through several cosmic processes and was present in the dust from which the Solar System formed.<ref>{{Cite journal |doi=10.1086/190111 |title=Nucleosynthesis of Heavy Elements by Neutron Capture |date=1965 |last1=Seeger |first1=Philip A. |last2=Fowler |first2=William A. |last3=Clayton |first3=Donald D. |journal=The Astrophysical Journal Supplement Series |volume=11 |page=121 |bibcode=1965ApJS...11..121S |url=http://tigerprints.clemson.edu/cgi/viewcontent.cgi?article=1307&context=physastro_pubs}}</ref> Scientists have identified three main cosmic sources for gold formation: supernova nucleosynthesis, neutron star collisions,<ref>{{cite news |url=https://pweb.cfa.harvard.edu/news/earths-gold-came-colliding-dead-stars |title=Earth's Gold Came from Colliding Dead Stars |work=David A. Aguilar & Christine Pulliam |publisher=cfa.harvard.edu |date=17 July 2013 |access-date=16 May 2025}}</ref> and magnetar flares.

All three sources involve a process called the r-process (rapid neutron capture), which forms elements heavier than iron.<ref>{{cite web |url=http://chandra.harvard.edu/xray_sources/supernovas.html |title=Supernovas & Supernova Remnants |publisher=Chandra X-ray Observatory |access-date=28 February 2014}}</ref> For decades, scientists believed supernova nucleosynthesis was the primary mechanism for gold formation. More recently, research has shown that neutron star collisions produce significant quantities of gold through the r-process.<ref>{{cite journal |last1=Berger |first1=E. |first2=W. |last2=Fong |first3=R. |last3=Chornock |date=2013 |title=An r-process Kilonova Associated with the Short-hard GRB 130603B |journal=The Astrophysical Journal Letters |volume=774 |issue=2 |page=4 |doi=10.1088/2041-8205/774/2/L23 |arxiv=1306.3960 |bibcode=2013ApJ...774L..23B|s2cid=669927 }}</ref>

In August 2017, the spectroscopic signatures of heavy elements, including gold, were directly observed by electromagnetic observatories during the GW170817 neutron star merger event.<ref>{{cite news |title=LIGO and Virgo make first detection of gravitational waves produced by colliding neutron stars |url=https://www.ligo.org/detections/GW170817/press-release/pr-english.pdf |archive-url=https://web.archive.org/web/20171031030151/http://www.ligo.org/detections/GW170817/press-release/pr-english.pdf |archive-date=31 October 2017 |url-status=live |publisher=LIGO & Virgo collaborations |date=16 October 2017 |access-date=15 February 2018}}</ref> This confirmed neutron star mergers as a source of gold, after years of only indirect detection.<ref>"we have no spectroscopic evidence that [such] elements have truly been produced," wrote author Stephan Rosswog.{{cite journal |last=Rosswog |first=Stephan |date=29 August 2013 |title=Astrophysics: Radioactive glow as a smoking gun |journal=Nature |volume=500 |issue=7464 |pages=535–536 |doi=10.1038/500535a |bibcode=2013Natur.500..535R |pmid=23985867|s2cid=4401544 }}</ref> This single event generated between 3 and 13 Earth masses of gold, suggesting that neutron star mergers might produce enough gold to account for most of this element in the universe.<ref>{{cite news |title=Neutron star mergers may create much of the universe's gold |work=Sid Perkins |publisher=Science AAAS |url=https://www.science.org/content/article/neutron-star-mergers-may-create-much-universe-s-gold |date=20 March 2018 |access-date=24 March 2018}}</ref>

However, neutron star mergers alone cannot explain all cosmic gold, particularly in older stars, because these mergers occur relatively late in galactic history and are infrequent (approximately once every 100,000 years).<ref>{{cite journal |last1=Patel |first1=Anirudh |last2=Metzger |first2=Brian D. |last3=Cehula |first3=Jakub |last4=Burns |first4=Eric |last5=Goldberg |first5=Jared A. |last6=Thompson |first6=Todd A. |title=Direct Evidence for r-process Nucleosynthesis in Delayed MeV Emission from the SGR 1806–20 Magnetar Giant Flare |journal=The Astrophysical Journal Letters |volume=984 |issue=1 |pages=L29 |date=April 29, 2025 |doi=10.3847/2041-8213/adc9b0 |doi-access=free |bibcode=2025ApJ...984L..29P }}</ref> This created a timing paradox in explaining the presence of gold in stars formed early in the universe.

In 2025, researchers resolved this paradox by confirming that giant flares from magnetars (highly magnetic neutron stars) are also a significant source of gold formation.<ref>{{cite journal |last1=Patel |first1=Anirudh |last2=Metzger |first2=Brian D. |last3=Cehula |first3=Jakub |last4=Burns |first4=Eric |last5=Goldberg |first5=Jared A. |last6=Thompson |first6=Todd A. |title=Direct Evidence for r-process Nucleosynthesis in Delayed MeV Emission from the SGR 1806–20 Magnetar Giant Flare |journal=The Astrophysical Journal Letters |volume=984 |issue=1 |pages=L29 |date=April 29, 2025 |doi=10.3847/2041-8213/adc9b0 |doi-access=free |bibcode=2025ApJ...984L..29P }}</ref> Analysis of a 2004 magnetar flare showed these events produce heavy elements through the same r-process as neutron star mergers. The amount of heavy elements created in a single magnetar flare can exceed the mass of Mars.<ref>{{cite news |last=Patel |first=Kasha |title=We figured out where gold comes from. The answer is explosive. |newspaper=The Washington Post |date=May 4, 2025 |url=https://www.washingtonpost.com/science/2025/05/04/first-gold-universe-heavy-metals-magnetar/ |access-date=May 5, 2025}}</ref> Since magnetars existed earlier in cosmic history and flare more frequently than neutron star mergers occur, they help explain gold's presence in older stars. Scientists estimate magnetar flares may contribute approximately 1-10% of all elements heavier than iron in our galaxy, including gold.<ref>{{cite news |title=Astronomers spot a gold mine in massive cosmic flares |work=Science.org |date=May 2025 |url=https://www.science.org/content/article/astronomers-spot-gold-mine-massive-cosmic-flares |access-date=May 5, 2025}}</ref>

=== Asteroid origin theories ===
Because the Earth was molten when it was formed, almost all of the gold present in the early Earth probably sank into the planetary core. Therefore, as hypothesized in one model, most of the gold in the Earth's crust and mantle is thought to have been delivered to Earth by asteroid impacts during the Late Heavy Bombardment, about 4 billion years ago.<ref name="Willbold-2011">{{cite journal |last2=Elliott |first2=Tim |last3=Moorbath |first3=Stephen |date=2011 |title=The tungsten isotopic composition of the Earth's mantle before the terminal bombardment |journal=Nature |volume=477 |issue=7363 |pages=195–8 |bibcode=2011Natur.477..195W |doi=10.1038/nature10399 |pmid=21901010 |last1=Willbold |first1=Matthias|s2cid=4419046 }}</ref><ref name="Battison-2011">{{cite news |url=https://www.bbc.co.uk/news/science-environment-14827624 |title=Meteorites delivered gold to Earth |last=Battison |first=Leila |date=8 September 2011 |work=BBC }}</ref>

Gold which is reachable by humans has, in one case, been associated with a particular asteroid impact. The asteroid that formed Vredefort impact structure 2.020 billion years ago is often credited with seeding the Witwatersrand basin in South Africa with the richest gold deposits on earth.<ref>{{cite web |url=http://superiormining.com/properties/south_africa/mangalisa/geology/ |title=Mangalisa Project |publisher=Superior Mining International Corporation |access-date=29 December 2014}}</ref><ref>{{cite journal |last1=Therriault |first1=A. M. |first2=R. A. F. |last2=Grieve |first3=W. U. |last3=Reimold |title=Original size of the Vredefort Structure: Implications for the geological evolution of the Witwatersrand Basin |journal=Meteoritics |volume=32 |pages=71–77 |date=1997 |bibcode=1997M&PS...32...71T |name-list-style=amp |doi=10.1111/j.1945-5100.1997.tb01242.x|doi-access=free }}</ref><ref>[https://web.archive.org/web/20120327184158/http://www.cosmosmagazine.com/news/2101/meteor-craters-may-hold-untapped-wealth Meteor craters may hold untapped wealth]. Cosmos Magazine (28 July 2008). Retrieved on 12 September 2013.</ref><ref>{{Cite journal |last1=Corner |first1=B. |last2=Durrheim |first2=R. J. |last3=Nicolaysen |first3=L. O. |title=Relationships between the Vredefort structure and the Witwatersrand basin within the tectonic framework of the Kaapvaal craton as interpreted from regional gravity and aeromagnetic data |doi=10.1016/0040-1951(90)90089-Q |journal=Tectonophysics |volume=171 |issue=1 |pages=49–61 |year=1990 |bibcode=1990Tectp.171...49C}}</ref> However, this scenario is now questioned. The gold-bearing Witwatersrand rocks were laid down between 700 and 950 million years before the Vredefort impact.<ref name="McCarthy-2005">McCarthy, T., Rubridge, B. (2005). ''The Story of Earth and Life''. Struik Publishers, Cape Town. pp. 89–90, 102–107, 134–136. {{ISBN|1 77007 148 2}}</ref><ref name="Norman-2006">Norman, N., Whitfield, G. (2006) ''Geological Journeys''. Struik Publishers, Cape Town. pp. 38–49, 60–61. {{ISBN|9781770070622}}</ref> These gold-bearing rocks had furthermore been covered by a thick layer of Ventersdorp lavas and the Transvaal Supergroup of rocks before the meteor struck, and thus the gold did not actually arrive in the asteroid/meteorite. What the Vredefort impact achieved, however, was to distort the Witwatersrand basin in such a way that the gold-bearing rocks were brought to the present erosion surface in Johannesburg, on the Witwatersrand, just inside the rim of the original {{cvt|300|km|adj=on}} diameter crater caused by the meteor strike. The discovery of the deposit in 1886 launched the Witwatersrand Gold Rush. Some 22% of all the gold that is ascertained to exist today on Earth has been extracted from these Witwatersrand rocks.<ref name="Norman-2006" />

=== Mantle return theories ===
Much of the rest of the gold on Earth is thought to have been incorporated into the planet since its very beginning, as planetesimals formed the mantle. In 2017, an international group of scientists established that gold "came to the Earth's surface from the deepest regions of our planet",<ref>{{cite web |author=University of Granada |title=Scientists reveal the mystery about the origin of gold |website=ScienceDaily |date=21 November 2017 |access-date=27 March 2018 |url=https://www.sciencedaily.com/releases/2017/11/171121095128.htm}}</ref> the mantle, as evidenced by their findings at Deseado Massif in the Argentinian Patagonia.<ref>{{cite journal |last1=Tassara |first1=Santiago |last2=González-Jiménez |first2=José M. |last3=Reich |first3=Martin |last4=Schilling |first4=Manuel E. |last5=Morata |first5=Diego |last6=Begg |first6=Graham |last7=Saunders |first7=Edward |last8=Griffin |first8=William L. |last9=O’Reilly |first9=Suzanne Y.|last10=Grégoire|first10=Michel |last11=Barra |first11=Fernando |last12=Corgne |first12=Alexandre |title=Plume-subduction interaction forms large auriferous provinces |journal=Nature Communications |volume=8 |issue=1 |pages=843 |year=2017 |issn=2041-1723 |doi=10.1038/s41467-017-00821-z |pmid=29018198 |pmc=5634996 |bibcode=2017NatCo...8..843T}}</ref>{{clarify|reason=this directly contradicts the first paragraph of the next section|date=April 2019}}

== Occurrence ==
[[File:Gold nugget (Australia) 4 (16848647509).jpg|thumb|left|upright=0.7|Native gold]]

On Earth, gold is found in ores in rock formed from the Precambrian time onward.<ref name="La Niece-2009" /> It most often occurs as a native metal, typically in a metal solid solution with silver (i.e. as a gold/silver alloy). Such alloys usually have a silver content of 8–10%. Electrum is elemental gold with more than 20% silver, and is commonly known as white gold. Electrum's color runs from golden-silvery to silvery, dependent upon the silver content. The more silver, the lower the specific gravity.
[[File:Gold-Pyrite-263192.jpg|thumb|left|upright=0.7|Gold in pyrite]]
Native gold occurs as very small to microscopic particles embedded in rock, often together with quartz or sulfide minerals such as "fool's gold", which is a pyrite.<ref>{{cite web |url=http://arizonagoldprospectors.com/formation.htm |title=Formation of Lode Gold Deposits |author=Heike, Brian |url-status=dead |archive-url=https://web.archive.org/web/20130122100747/http://arizonagoldprospectors.com/formation.htm |archive-date=22 January 2013 |publisher=Arizona Gold Prospectors|access-date=24 February 2021}}</ref> These are called lode deposits. The metal in a native state is also found in the form of free flakes, grains or larger nuggets<ref name="La Niece-2009" /> that have been eroded from rocks and end up in alluvial deposits called placer deposits. Such free gold is always richer at the exposed surface of gold-bearing veins, owing to the oxidation of accompanying minerals followed by weathering; and by washing of the dust into streams and rivers, where it collects and can be welded by water action to form nuggets.

Gold sometimes occurs combined with tellurium as the minerals calaverite, krennerite, nagyagite, petzite and sylvanite (see telluride minerals), and as the rare bismuthide maldonite ({{chem2|Au2Bi}}) and antimonide aurostibite ({{chem2|AuSb2}}). Gold also occurs in rare alloys with copper, lead, and mercury: the minerals auricupride ({{chem2|Cu3Au}}), novodneprite ({{chem2|AuPb3}}) and weishanite ({{chem2|(Au,Ag)3Hg2}}).

A 2004 research paper suggests that microbes can sometimes play an important role in forming gold deposits, transporting and precipitating gold to form grains and nuggets that collect in alluvial deposits.<ref>{{cite web |url=http://www.abc.net.au/science/news/enviro/EnviroRepublish_1032376.htm |title=Environment & Nature News – Bugs grow gold that looks like coral |date=28 January 2004 |access-date=22 July 2006 |publisher=abc.net.au}} This is doctoral research undertaken by Frank Reith at the Australian National University, published 2004.</ref>

A 2013 study has claimed water in faults vaporizes during an earthquake, depositing gold. When an earthquake strikes, it moves along a fault. Water often lubricates faults, filling in fractures and jogs. About {{convert|10|km}} below the surface, under very high temperatures and pressures, the water carries high concentrations of carbon dioxide, silica, and gold. During an earthquake, the fault jog suddenly opens wider. The water inside the void instantly vaporizes, flashing to steam and forcing silica, which forms the mineral quartz, and gold out of the fluids and onto nearby surfaces.<ref>{{cite web |url=https://news.yahoo.com/earthquakes-turn-water-gold-180356174.html |title=Earthquakes Turn Water into Gold |date=17 March 2013 |access-date=18 March 2013}}</ref>

=== Seawater ===
The world's oceans contain gold. Measured concentrations of gold in the Atlantic and Northeast Pacific are 50–150 femtomol/L or 10–30 parts per quadrillion (about 10–30 g/km3). In general, gold concentrations for south Atlantic and central Pacific samples are the same (~50 femtomol/L) but less certain. Mediterranean deep waters contain slightly higher concentrations of gold (100–150 femtomol/L), which is attributed to wind-blown dust or rivers. At 10 parts per quadrillion, the Earth's oceans would hold 15,000 tonnes of gold.<ref>{{Cite journal |doi=10.1016/0012-821X(90)90060-B |title=Gold in seawater |first1=K. |last1=Kenison Falkner |author-link1=Kelly Falkner|journal=Earth and Planetary Science Letters |volume=98 |date=1990 |pages=208–221 |last2=Edmond |first2=J. |issue=2 |bibcode=1990E&PSL..98..208K}}</ref> These figures are three orders of magnitude less than reported in the literature prior to 1988, indicating contamination problems with the earlier data.

A number of people have claimed to be able to economically recover gold from sea water, but they were either mistaken or acted in an intentional deception. Prescott Jernegan ran a gold-from-seawater swindle in the United States in the 1890s, as did an English fraudster in the early 1900s.<ref>Plazak, Dan ''A Hole in the Ground with a Liar at the Top'' (Salt Lake: Univ. of Utah Press, 2006) {{ISBN|0-87480-840-5}} (contains a chapter on gold-from seawater swindles)</ref> Fritz Haber did research on the extraction of gold from sea water in an effort to help pay Germany's reparations following World War I.<ref>{{Cite journal |title=Das Gold im Meerwasser |first=F. |last=Haber |volume=40 |issue=11 |date=1927 |doi=10.1002/ange.19270401103 |pages=303–314 |journal=Zeitschrift für Angewandte Chemie|bibcode=1927AngCh..40..303H }}</ref> Based on the published values of 2 to 64 ppb of gold in seawater, a commercially successful extraction seemed possible. After analysis of 4,000 water samples yielding an average of 0.004 ppb, it became clear that extraction would not be possible, and he ended the project.<ref>{{Cite journal |doi=10.1016/0375-6742(88)90051-9 |title=Concentration of gold in natural waters |first=J. B. |last=McHugh |journal=Journal of Geochemical Exploration |volume=30 |date=1988 |pages=85–94 |issue=1–3 |bibcode=1988JCExp..30...85M |url=https://zenodo.org/record/1258491 |archive-url=https://web.archive.org/web/20200307233511/https://zenodo.org/record/1258491 |url-status=dead |archive-date=7 March 2020}}</ref>

== History ==
[[File:Grave offerings.jpg|thumb|Oldest golden artifacts in the world (4600–4200 BC) from Varna necropolis, Bulgaria — grave offerings on exposition in Varna Museum.]]
[[File:Indian gold tribute donor Apadana.jpg|thumb|upright|An Indian tribute-bearer at Apadana, from the Achaemenid satrapy of ''Hindush'', carrying gold on a yoke, circa 500 BC.<ref name="Iran-1972">"Furthermore the second member of Delegation XVIII is carrying four small but evidently heavy jars on a yoke, probably containing the gold dust which was the tribute paid by the Indians." in {{cite book |last1=Iran |first1=Délégation archéologique française en |title=Cahiers de la Délégation archéologique française en Iran |date=1972 |publisher=Institut français de recherches en Iran (section archéologique) |pages=146 |url=https://books.google.com/books?id=itIRAQAAMAAJ}}</ref>]]

[[File:Gold Museum, Bogota (36145671394).jpg|thumb|right|The Muisca raft, between circa 600–1600 AD. The figure refers to the ceremony of the legend of El Dorado. The ''zipa'' used to cover his body in gold dust, and from his raft, he offered treasures to the ''Guatavita'' goddess in the middle of the sacred lake. This old Muisca tradition became the origin of the legend of El Dorado. This Muisca raft figure is on display in the Gold Museum, Bogotá, Colombia.]]

The earliest recorded metal employed by humans appears to be gold, which can be found free or "native". Small amounts of natural gold have been found in Spanish caves used during the late Paleolithic period, {{Circa|40,000 BC}}.<ref>{{Cite book |last=Yannopoulos |first=J. C. |url=https://books.google.com/books?id=hE7uBwAAQBAJ&dq=history+of+gold+begins+in+antiquity.+Bits+of+gold+were+found+in+Spanish+caves+that+were+used+by+Paleolithic+people+around+40,000+B.C.&pg=PP8 |title=The Extractive Metallurgy of Gold |publisher=Springer US |year=1991 |isbn=978-1-4684-8427-4 |location=Boston, MA |pages=ix |language=en |doi=10.1007/978-1-4684-8425-0}}</ref>

The oldest gold artifacts in the world are from Bulgaria and are dating back to the 5th millennium BC (4,600 BC to 4,200 BC), such as those found in the Varna Necropolis near Lake Varna and the Black Sea coast, thought to be the earliest "well-dated" finding of gold artifacts in history.<ref>{{cite web | url=https://www.smithsonianmag.com/travel/varna-bulgaria-gold-graves-social-hierarchy-prehistoric-archaelogy-smithsonian-journeys-travel-quarterly-180958733/ | title=Mystery of the Varna Gold: What Caused These Ancient Societies to Disappear? }}</ref><ref name="La Niece-2009">{{cite book |last=La Niece |first=Susan (senior metallurgist in the British Museum Department of Conservation and Scientific Research) |url=https://books.google.com/books?id=oAfITjcHiZ0C |title=Gold |page=10 |publisher=Harvard University Press |access-date=10 April 2012 |isbn=978-0-674-03590-4 |date=15 December 2009}}</ref><ref>{{cite web | url=https://www.smithsonianmag.com/smart-news/oldest-gold-object-unearthed-bulgaria-180960093/ | title=World's Oldest Gold Object May Have Just Been Unearthed in Bulgaria }}</ref>

Gold artifacts probably made their first appearance in Ancient Egypt at the very beginning of the pre-dynastic period, at the end of the fifth millennium BC and the start of the fourth, and smelting was developed during the course of the 4th millennium; gold artifacts appear in the archeology of Lower Mesopotamia during the early 4th millennium.<ref>Sutherland, C.H.V, Gold (London, Thames & Hudson, 1959) p 27 ff.</ref> As of 1990, gold artifacts found at the Wadi Qana cave cemetery of the 4th millennium BC in West Bank were the earliest from the Levant.<ref name="Gopher-1990">{{cite journal |last1=Gopher |first1=A. |first2=T. |last2=Tsuk |first3=S. |last3=Shalev |first4=R. |last4=Gophna |name-list-style=amp |title=Earliest Gold Artifacts in the Levant |date=August–October 1990 |journal=Current Anthropology |volume=31 |issue=4 |pages=436–443 |jstor=2743275 |doi=10.1086/203868|s2cid=143173212 }}</ref> Gold artifacts such as the golden hats and the Nebra disk appeared in Central Europe from the 2nd millennium BC Bronze Age.

The oldest known map of a gold mine was drawn in the 19th Dynasty of Ancient Egypt (1320–1200 BC), whereas the first written reference to gold was recorded in the 12th Dynasty around 1900 BC.<ref>Pohl, Walter L. (2011) ''Economic Geology Principles and Practice''. Wiley. p. 208. {{doi|10.1002/9781444394870.ch2}}. {{ISBN|9781444394870 }}</ref> Egyptian hieroglyphs from as early as 2600 BC describe gold, which King Tushratta of the Mitanni claimed was "more plentiful than dirt" in Egypt.<ref>{{cite book |last1=Montserrat |first1=Dominic |url=https://books.google.com/books?id=bfRbY4gInsQC |title=Akhenaten: History, Fantasy and Ancient Egypt |isbn=978-0-415-30186-2 |date=21 February 2003|publisher=Psychology Press }}</ref> Egypt and especially Nubia had the resources to make them major gold-producing areas for much of history. One of the earliest known maps, known as the Turin Papyrus Map, shows the plan of a gold mine in Nubia together with indications of the local geology. The primitive working methods are described by both Strabo and Diodorus Siculus, and included fire-setting. Large mines were also present across the Red Sea in what is now Saudi Arabia.

[[File:Golden crown Armento Staatliche Antikensammlungen 01.jpg|thumb|left|Ancient golden Kritonios Crown, funerary or marriage material, 370–360 BC; from a grave in Armento, Basilicata]]
Gold is mentioned in the Amarna letters numbered 19<ref>Moran, William L., 1987, 1992. The Amarna Letters, pp. 43–46.</ref> and 26<ref>Moran, William L. 1987, 1992. The Amarna Letters. EA 245, "To the Queen Mother: Some Missing Gold Statues", pp. 84–86.</ref> from around the 14th century BC.<ref>[https://www.britannica.com/biography/Akhenaten "Akhenaten"] {{Webarchive|url=https://web.archive.org/web/20080611092705/http://www.britannica.com/eb/article-9005276/Akhenaton |date=11 June 2008 }}. ''Encyclopaedia Britannica''</ref><ref>Dodson, Aidan and Hilton, Dyan (2004). ''The Complete Royal Families of Ancient Egypt''. Thames & Hudson. {{ISBN|0-500-05128-3}}</ref>

Gold is mentioned frequently in the Old Testament, starting with Genesis 2:11 (at Havilah), the story of the golden calf, and many parts of the temple including the Menorah and the golden altar. In the New Testament, it is included with the gifts of the magi in the first chapters of Matthew. The Book of Revelation 21:21 describes the city of New Jerusalem as having streets "made of pure gold, clear as crystal". Exploitation of gold in the south-east corner of the Black Sea is said to date from the time of Midas, and this gold was important in the establishment of what is probably the world's earliest coinage in Lydia around 610 BC.<ref name="Lion-2003" /> The legend of the golden fleece dating from eighth century BCE may refer to the use of fleeces to trap gold dust from placer deposits in the ancient world. From the 6th or 5th century BC, the Chu (state) circulated the Ying Yuan, one kind of square gold coin.

In Roman metallurgy, new methods for extracting gold on a large scale were developed by introducing hydraulic mining methods, especially in Hispania from 25 BC onwards and in Dacia from 106 AD onwards. One of their largest mines was at Las Medulas in León, where seven long aqueducts enabled them to sluice most of a large alluvial deposit. The mines at Roşia Montană in Transylvania were also very large, and until very recently,{{when|date=January 2024}} still mined by opencast methods. They also exploited smaller deposits in Britain, such as placer and hard-rock deposits at Dolaucothi. The various methods they used are well described by Pliny the Elder in his encyclopedia ''Naturalis Historia'' written towards the end of the first century AD.

During Mansa Musa's (ruler of the Mali Empire from 1312 to 1337) hajj to Mecca in 1324, he passed through Cairo in July 1324, and was reportedly accompanied by a camel train that included thousands of people and nearly a hundred camels where he gave away so much gold that it depressed the price in Egypt for over a decade, causing high inflation.<ref>[https://web.archive.org/web/20060524015912/http://www.blackhistorypages.net/pages/mansamusa.php Mansa Musa]. Black History Pages</ref> A contemporary Arab historian remarked:

{{blockquote|Gold was at a high price in Egypt until they came in that year. The mithqal did not go below 25 dirhams and was generally above, but from that time its value fell and it cheapened in price and has remained cheap till now. The mithqal does not exceed 22 dirhams or less. This has been the state of affairs for about twelve years until this day by reason of the large amount of gold which they brought into Egypt and spent there [...].|sign=Chihab Al-Umari|source=Kingdom of Mali<ref>{{cite web |title=Kingdom of Mali – Primary Source Documents |url=http://www.bu.edu/africa/outreach/resources/k_o_mali/ |website=African studies Center |publisher=Boston University |access-date=30 January 2012}}</ref>}}

[[File:Monnaie de Bactriane, Eucratide I, 2 faces.jpg|thumb|Gold coin of Eucratides I (171–145 BC), one of the Hellenistic rulers of ancient Ai-Khanoum. This is the largest known gold coin minted in antiquity ({{cvt|169.2|g}}; {{cvt|58|mm}}).<ref>{{cite book |last1=Monnaie |first1=Eucratide I. (roi de Bactriane) Autorité émettrice de |title=[Monnaie : 20 Statères, Or, Incertain, Bactriane, Eucratide I] |url=https://gallica.bnf.fr/ark:/12148/btv1b8510709q}}</ref>]]
The European exploration of the Americas was fueled in no small part by reports of the gold ornaments displayed in great profusion by Native American peoples, especially in Mesoamerica, Peru, Ecuador and Colombia. The Aztecs regarded gold as the product of the gods, calling it literally "god excrement" (''teocuitlatl'' in Nahuatl), and after Moctezuma II was killed, most of this gold was shipped to Spain.<ref>{{Cite book |first1=Frances |last1=Berdan |first2=Patricia Rieff |last2=Anawalt |title=The Codex Mendoza |volume=2 |page=151 |publisher=University of California Press |date=1992 |isbn=978-0-520-06234-4}}</ref> However, for the indigenous peoples of North America gold was considered useless and they saw much greater value in other minerals which were directly related to their utility, such as obsidian, flint, and slate.<ref>[https://web.archive.org/web/20120112010110/http://www.sierranevadavirtualmuseum.com/docs/galleries/history/culture/shadows.htm Sierra Nevada Virtual Museum]. Sierra Nevada Virtual Museum. Retrieved on 4 May 2012.</ref>

El Dorado is applied to a legendary story in which precious stones were found in fabulous abundance along with gold coins. The concept of El Dorado underwent several transformations, and eventually accounts of the previous myth were also combined with those of a legendary lost city. El Dorado, was the term used by the Spanish Empire to describe a mythical tribal chief (zipa) of the Muisca native people in Colombia, who, as an initiation rite, covered himself with gold dust and submerged in Lake Guatavita. The legends surrounding El Dorado changed over time, as it went from being a man, to a city, to a kingdom, and then finally to an empire.{{cn|date=January 2024}}

Beginning in the early modern period, European exploration and colonization of West Africa was driven in large part by reports of gold deposits in the region, which was eventually referred to by Europeans as the "Gold Coast".<ref>{{cite book | first=James Maxwell | last=Anderson|title=The History of Portugal | publisher=Greenwood Publishing Group | year=2000 | isbn=0-313-31106-4 | url=https://books.google.com/books?id=UoryGn9o4x0C | ref=refAnderson}}</ref> From the late 15th to early 19th centuries, European trade in the region was primarily focused in gold, along with ivory and slaves.<ref>{{Cite book|last=Newitt|first=Malyn|url=https://books.google.com/books?id=fsoWg1yXKQUC&q=portuguese+in+ghana|title=The Portuguese in West Africa, 1415–1670: A Documentary History|date=28 June 2010|publisher=Cambridge University Press|isbn=978-1-139-49129-7|language=en}}</ref> The gold trade in West Africa was dominated by the Ashanti Empire, who initially traded with the Portuguese before branching out and trading with British, French, Spanish and Danish merchants.<ref name="Green-2019">{{cite book |last1=Green |first1=Toby |title=A fistful of shells : West Africa from the rise of the slave trade to the age of revolution |date=31 January 2019 |location=London |isbn=978-0-241-00328-2 |pages=108, 247 |edition=Penguin Books Ltd. Kindle-Version}}</ref> British desires to secure control of West African gold deposits played a role in the Anglo-Ashanti wars of the late 19th century, which saw the Ashanti Empire annexed by Britain.<ref>{{cite book |last=Edgerton |first=Robert B. |year=2010 |title=The Fall of the Asante Empire: The Hundred-Year War For Africa's Gold Coast |publisher=Simon and Schuster |isbn=978-1-4516-0373-6 }}</ref>

Gold played a role in western culture, as a cause for desire and of corruption, as told in children's fables such as Rumpelstiltskin—where Rumpelstiltskin turns hay into gold for the peasant's daughter in return for her child when she becomes a princess—and the stealing of the hen that lays golden eggs in Jack and the Beanstalk.

The top prize at the Olympic Games and many other sports competitions is the gold medal.

75% of the presently accounted for gold has been extracted since 1910, two-thirds since 1950.{{ref needed|date=May 2024}}

One main goal of the alchemists was to produce gold from other substances, such as lead — presumably by the interaction with a mythical substance called the philosopher's stone. Trying to produce gold led the alchemists to systematically find out what can be done with substances, and this laid the foundation for today's chemistry, which can produce gold (albeit uneconomically) by using nuclear transmutation.<ref>{{cite web |url=https://www.scientificamerican.com/article/fact-or-fiction-lead-can-be-turned-into-gold/ |title=Fact or Fiction?: Lead Can Be Turned into Gold |author=Matson, John |date=31 January 2014 |website=scientificamerican.com |access-date=21 November 2021}}</ref> Their symbol for gold was the circle with a point at its center (☉), which was also the astrological symbol and the ancient Chinese character for the Sun.

The Dome of the Rock is covered with an ultra-thin golden glassier. The Sikh Golden temple, the Harmandir Sahib, is a building covered with gold. Similarly the Wat Phra Kaew emerald Buddhist temple (wat) in Thailand has ornamental gold-leafed statues and roofs. Some European king and queen's crowns were made of gold, and gold was used for the bridal crown since antiquity. An ancient Talmudic text circa 100 AD describes Rachel, wife of Rabbi Akiva, receiving a "Jerusalem of Gold" (diadem). A Greek burial crown made of gold was found in a grave circa 370 BC.

<gallery mode="packed" heights="170px">
Gold leaf MET DP260372.jpg|Minoan jewellery, 2300–2100 BC, gold, Metropolitan Museum of Art, New York
Earrings from Shulgi.JPG|Sumerian earrings with cuneiform inscriptions, 2093–2046 BC, gold, Sulaymaniyah Museum, Sulaymaniyah, Iraq
File:Aegina treasure 10.jpg|Minoan cup, part of the Aegina Treasure, 1850–1550 BC, gold, British Museum<ref>{{cite book|last1=La Niece|first1=Susan|title=Gold|date=2009|publisher=The British Museum Press|isbn=978-0-7141-5076-5|page=8|url=|language=en}}</ref>
Statuette of Amun MET DT553.jpg|Ancient Egyptian statuette of Amun, 945–715 BC, gold, Metropolitan Museum of Art
Anillo de Sheshonq (46627183381).jpg|Ancient Egyptian signet ring, 664–525 BC, gold, British Museum
File:Openwork dagger handle-IMG 4418-black.jpg|Ancient Chinese cast openwork dagger hilt, 6th–5th centuries BC, gold, British Museum<ref>{{cite book|last1=La Niece|first1=Susan|title=Gold|date=2009|publisher=The British Museum Press|isbn=978-0-7141-5076-5|page=25|url=|language=en}}</ref>
Gold stater MET DP138743.jpg|Ancient Greek stater, 323–315 BC, gold, Metropolitan Museum of Art
Gold funerary wreath MET DP257471.jpg|Etruscan funerary wreath, 4th–3rd century BC, gold, Metropolitan Museum of Art
Gold aureus of Hadrian MET DP104782b.jpg|Roman aureus of Hadrian, 134–138 AD, gold, Metropolitan Museum of Art
Lime Container (Poporo) MET DT1262.jpg|Quimbaya lime container, 5th–9th century, gold, Metropolitan Museum of Art
File:British Museum - Room 41 (20626313758).jpg|Anglo-Saxon belt buckle from Sutton Hoo with a niello interlace pattern, 7th century, gold, British Museum<ref>{{cite book|last1=La Niece|first1=Susan|title=Gold|date=2009|publisher=The British Museum Press|isbn=978-0-7141-5076-5|page=76|url=|language=en}}</ref>
Byzantium, 11th century - Scyphate - 2001.25 - Cleveland Museum of Art.tif|Byzantine scyphate, 1059–1067, gold, Cleveland Museum of Art, Cleveland, Ohio, USA
Double Bat-Head Figure Pendant MET DT935.jpg|Pre-Columbian pendant with two bat-head warriors who carry spears, 11th–16th century, gold, Metropolitan Museum of Art
File:AHOTWgold lama.JPG|Inca hollow model of a llama, 14th-15th centuries, gold, British Museum<ref>{{cite book|last1=La Niece|first1=Susan|title=Gold|date=2009|publisher=The British Museum Press|isbn=978-0-7141-5076-5|page=66|url=|language=en}}</ref>
File:The Judgement of Paris, Waddeson Bequest.jpg|Renaissance hat badge that shows the Judgment of Paris, 16th century, enamelled gold, British Museum<ref>{{cite book|last1=La Niece|first1=Susan|title=Gold|date=2009|publisher=The British Museum Press|isbn=978-0-7141-5076-5|page=20|url=|language=en}}</ref>
Box with scene depicting Roman hero Gaius Mucius Scaevola before the Etruscan king Lars Porsena MET DP170836 (cropped).jpg|Rococo box, by George Michael Moser, 1741, gold, Metropolitan Museum of Art
Jean Joseph de Saint-Germain - Candelabrum - 1946.81 - Cleveland Museum of Art.tif|Rococo candelabrum, by Jean Joseph de Saint-Germain, {{circa}}1750, gilt bronze, Cleveland Museum of Art
Tabatière Minerve, Mercure, Pégase (Louvre, OA 2121).jpg|Rococo snuff box with Minerva, by Jean-Malquis Lequin, 1750–1752, gold and painted enamel, Louvre<ref>{{cite web|url=https://collections.louvre.fr/en/ark:/53355/cl010111221|website=collections.louvre.fr|title=Tabatière|access-date=18 November 2023}}</ref>
File:Tabatière J-Frémin (Louvre, OA 6857).jpg|Louis XVI style snuff box, by Jean Frémin, 1763–1764, gold and painted enamel, Louvre<ref>{{cite web|url=https://collections.louvre.fr/en/ark:/53355/cl010099410|website=collections.louvre.fr|title=Tabatière ovale|access-date=18 November 2023}}</ref>
File:Washstand (athénienne or lavabo) MET DP106594.jpg|Neoclassical washstand (athénienne or lavabo), 1800–1814, legs, base and shelf of yew wood, gilt bronze mounts, iron plate beneath shelf, Metropolitan Museum of Art
File:Clock, French, circa 1835-1840, gilt and patinated bronze, inherited from Maurice Quentin Bauchart, 1911, inv. 17741, Museum of Decorative Arts, Paris.jpg|Gothic Revival clock, unknown French maker, {{circa}}1835-1840, gilt and patinated bronze, Museum of Decorative Arts, Paris
File:Teapot, by Alphonse Debain, from Paris, 1900, gilt silver and ivory, inv. 2021.63.1 MAD Paris.jpg|Art Nouveau teapot, by Alphonse Debain, gilt silver and ivory, Museum of Decorative Arts
</gallery>

=== Etymology ===
[[File:Beowulf - gold.jpg|thumb|An early mention of gold in the ''Beowulf'']]
''Gold'' is cognate with similar words in many Germanic languages, deriving via Proto-Germanic *''gulþą'' from Proto-Indo-European *''ǵʰelh₃-'' {{gloss|to shine, to gleam; to be yellow or green}}.<ref>{{OEtymD|gold}}</ref><ref>Hesse, R W. (2007) [https://books.google.com/books?id=DIWEi5Hg93gC&pg=PA103 Jewelrymaking Through History: An Encyclopedia] {{Webarchive|url=https://web.archive.org/web/20221101113823/https://books.google.com/books?id=DIWEi5Hg93gC&pg=PA103 |date=1 November 2022 }}, Greenwood Publishing Group. {{ISBN|0313335079}}</ref>

The symbol ''Au'' is from the Latin {{lang|la|aurum}} {{gloss|gold}}.<ref>Notre Dame University [http://www.archives.nd.edu/cgi-bin/lookup.pl?stem=Aurum&ending= Latin Dictionary] {{Webarchive|url=https://web.archive.org/web/20160205123228/http://www.archives.nd.edu/cgi-bin/lookup.pl?stem=Aurum&ending= |date=5 February 2016 }} Retrieved 7 June 2012</ref> The Proto-Indo-European ancestor of ''aurum'' was ''*h₂é-h₂us-o-'', meaning {{gloss|glow}}. This word is derived from the same root (Proto-Indo-European ''*h₂u̯es-'' {{gloss|to dawn}}) as ''*h₂éu̯sōs'', the ancestor of the Latin word {{lang|la|aurora}} {{gloss|dawn}}.<ref>{{cite book |last=de Vaan |first=Michel |title=Etymological Dictionary of Latin and the other Italic languages |date=2008 |publisher=Brill |location=Leiden: Boston |isbn=978-90-04-16797-1 |page=63}}</ref> This etymological relationship is presumably behind the frequent claim in scientific publications that {{lang|la|aurum}} meant {{gloss|shining dawn}}.<ref name="Christie-2011">Christie, A and Brathwaite, R. (Last updated 2 November 2011) [https://web.archive.org/web/20130208092020/http://www.nzpam.govt.nz/cms/pdf-library/minerals/publications/Commodity%20Reports/report14_gold.pdf Mineral Commodity Report 14 — Gold], Institute of geological and Nuclear sciences Ltd – Retrieved 7 June 2012</ref>

=== Culture ===
{{anchor|Cultural history}}
[[File:Jewelry and clothing ornaments.jpg|thumb|Gold crafts from the Philippines prior to Western contact]]
In popular culture gold is a high standard of excellence, often used in awards.<ref name="Jansen-2008" /> Great achievements are frequently rewarded with gold, in the form of gold medals, gold trophies and other decorations. Winners of athletic events and other graded competitions are usually awarded a gold medal. Many awards such as the Nobel Prize are made from gold as well. Other award statues and prizes are depicted in gold or are gold plated (such as the Academy Awards, the Golden Globe Awards, the Emmy Awards, the Palme d'Or, and the British Academy Film Awards).<ref>H. G. Bachmann, ''The lure of gold : an artistic and cultural history'' (2006).</ref>

Aristotle in his ethics used gold symbolism when referring to what is now known as the golden mean. Similarly, gold is associated with perfect or divine principles, such as in the case of the golden ratio and the Golden Rule. Gold is further associated with the wisdom of aging and fruition. The fiftieth wedding anniversary is golden. A person's most valued or most successful latter years are sometimes considered "golden years" or "golden jubilee". The height of a civilization is referred to as a golden age.<ref>Lubna Umar and Sarwet Rasul, "Critical Metaphor Analysis: Nawaz Sharif and the Myth of a Golden Time" ''NUML Journal of Critical Inquiry'' 15#2, (Dec 2017): 78–102.</ref>

==== Religion ====
[[File:Filippine, provincia di agusan, immagine hindu, statuetta in oro massiccio, xiii secolo.jpg|thumb|The Agusan image, depicting a deity from northeast Mindanao]]
The first known prehistoric human usages of gold were religious in nature.<ref>{{Cite web |last=Lioudis |first=Nick |date=30 April 2023 |title=What Is the Gold Standard? Advantages, Alternatives, and History |url=https://www.investopedia.com/ask/answers/09/gold-standard.asp |access-date=21 September 2023 |website=Investopedia |language=en}}</ref>

In some forms of Christianity and Judaism, gold has been associated both with the sacred and evil. In the Book of Exodus, the Golden Calf is a symbol of idolatry, while in the Book of Genesis, Abraham was said to be rich in gold and silver, and Moses was instructed to cover the Mercy Seat of the Ark of the Covenant with pure gold. In Byzantine iconography the halos of Christ, Virgin Mary and the saints are often golden.<ref>{{cite journal | last1 = Alborn | first1 = Timothy | year = 2017 | title = The Greatest Metaphor Ever Mixed: Gold in the British Bible, 1750–1850 | url = https://academicworks.cuny.edu/le_pubs/184| journal = Journal of the History of Ideas | volume = 78 | issue = 3| pages = 427–447 | doi = 10.1353/jhi.2017.0024 | pmid = 28757488 | s2cid = 27312741 }}</ref>

In Islam,<ref name="Moors-2013">{{cite journal |last1=Moors |first1=Annelies |title=Wearing gold, owning gold: the multiple meanings of gold jewelry |journal=Etnofoor |date=2013 |volume=25 |issue=1 |pages=78–89 |oclc=858949147|issn=0921-5158}}</ref> gold (along with silk)<ref name="Boulanouar-2011">{{cite thesis |last1=Boulanouar |first1=Aisha Wood |url=http://hdl.handle.net/10523/1748|title=Myths and Reality: Meaning in Moroccan Muslim Women's Dress |date=2011 |publisher=University of Otago |hdl=10523/1748 |type=Thesis, Doctor of Philosophy|citeseerx=10.1.1.832.2031 }}</ref><ref name="Poonai-2015">{{cite web |last1=Poonai |first1=Anand |title=Islamic Male Clothing |url=https://eportfolios.macaulay.cuny.edu/whatwewear/men/ |website=Who We Are & What We Wear |access-date=17 June 2020 |date=2015}}</ref> is often cited as being forbidden for men to wear.<ref name="Aziz-2010">{{cite journal |last1=Aziz |first1=Rookhsana |url=http://hdl.handle.net/10500/4888 |title=Hijab – The Islamic Dress Code: Its historical development, evidence from sacred sources and views of selected Muslim scholars |date=November 2010 |publisher=University of South Africa|journal=UNISA EDT (Electronic Theses and Dissertations)|hdl=10500/4888 |type=Thesis, Master of Arts|citeseerx=10.1.1.873.8651 }}</ref> Abu Bakr al-Jazaeri, quoting a hadith, said that "[t]he wearing of silk and gold are forbidden on the males of my nation, and they are lawful to their women".<ref name="Toronto-2001">{{cite journal |last1=Toronto |first1=James A. |title=Many Voices, One ''Umma'': Sociopolitical Debate in the Muslim Community |journal=BYU Studies Quarterly |date=1 October 2001 |volume=40 |issue=4 |pages=29–50 |url=https://scholarsarchive.byu.edu/byusq/vol40/iss4/4}}</ref> This, however, has not been enforced consistently throughout history, e.g. in the Ottoman Empire.<ref name="Jirousek-2004">{{cite web |last1=Jirousek |first1=Charlotte |title=Islamic Clothing |url=http://char.txa.cornell.edu/islamicclothes.htm |publisher=Encyclopedia of Islam |access-date=17 June 2020 |date=2004}}</ref> Further, small gold accents on clothing, such as in embroidery, may be permitted.<ref name="Omar-2014">{{cite journal |last1=Omar |first1=Sara |title=Dress |journal=The Encyclopedia of Islam and Law, Oxford Islamic Studies Online |date=28 March 2014 |url=https://www.oxfordislamicstudies.com/article/opr/t349/e0040 }} {{dead link|date=December 2021 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

In ancient Greek religion and mythology, Theia was seen as the goddess of gold, silver and other gemstones.<ref>{{cite book | page = [https://books.google.com/books?id=c7cNB-JaZA8C&pg=PT153 153] | last1 = Daly | last2 = Rengel | title = Greek and Roman Mythology, A to Z | first1 = Kathleen N. | first2 = Marian | publisher = Chelsea House Publishers | date = 1992 | isbn = 978-1-60413-412-4}}</ref>

According to Christopher Columbus, those who had something of gold were in possession of something of great value on Earth and a substance to even help souls to paradise.<ref>{{cite book |last=Bernstein |first=Peter L. |url=https://books.google.com/books?id=dIYmHiYhDu8C |title=The Power of Gold: The History of an Obsession |date=2004 |publisher=John Wiley & Sons |isbn=978-0-471-43659-1 |page=1}}</ref>

Wedding rings are typically made of gold. It is long lasting and unaffected by the passage of time and may aid in the ring symbolism of eternal vows before God and the perfection the marriage signifies. In Orthodox Christian wedding ceremonies, the wedded couple is adorned with a golden crown (though some opt for wreaths, instead) during the ceremony, an amalgamation of symbolic rites.{{Explain|reason=Is it a single crown and where does the amalgamation come from?|date=September 2023}}

On 24 August 2020, Israeli archaeologists discovered a trove of early Islamic gold coins near the central city of Yavne. Analysis of the extremely rare collection of 425 gold coins indicated that they were from the late 9th century. Dating to around 1,100 years back, the gold coins were from the Abbasid Caliphate.<ref>{{cite web|url=https://apnews.com/5a35414a3fdcdf42c68a274b69595750|title=Israeli dig unearths large trove of early Islamic gold coins|access-date=24 August 2020|website=Associated Press|date=24 August 2020 }}</ref>

== Production ==
{{Main|List of countries by gold production}}
[[File:Gold - world production trend.svg|thumb|lang=en|Time trend of gold production|link=File:Gold_-_world_production_trend.svg%3Flang=en]]
According to the United States Geological Survey in 2016, about {{convert|5,726,000,000|ozt|t}} of gold has been accounted for, of which 85% remains in active use.<ref>{{cite report |first1=John L. |last1=Munteen |first2=David A. |last2=Davis |first3=Bridget |last3=Ayling |date=2017 |title=The Nevada Mineral Industry 2016 |url=http://epubs.nsla.nv.gov/statepubs/epubs/210988-2016.pdf |publisher=University of Nevada, Reno |access-date=9 February 2019 |oclc=1061602920 |archive-url=https://web.archive.org/web/20190209232131/http://epubs.nsla.nv.gov/statepubs/epubs/210988-2016.pdf |archive-date=9 February 2019 |url-status=dead }}</ref>

=== Mining and prospecting ===
{{Main|Gold mining|Gold prospecting}}
[[File:Miner underground at Pumsaint gold mine (1294028).jpg|thumb|left|A miner underground at Pumsaint gold mine, Wales; {{Circa|1938}}.]]
[[File:Grasberg mine.jpg|upright=1|thumb|Grasberg mine, Indonesia is the world's largest gold mine.]]
Since the 1880s, South Africa has been the source of a large proportion of the world's gold supply, and about 22% of the gold presently accounted is from South Africa. Production in 1970 accounted for 79% of the world supply, about 1,480 tonnes. In 2007 China (with 276 tonnes) overtook South Africa as the world's largest gold producer, the first time since 1905 that South Africa had not been the largest.<ref>{{cite web |last=Mandaro |first=Laura |url=http://www.marketwatch.com/story/china-now-worlds-largest-gold-producer-foreign-miners-at-door |title=China now world's largest gold producer; foreign miners at door |website=MarketWatch |date=17 January 2008 |access-date=5 April 2009}}</ref>

In 2023, China was the world's leading gold-mining country, followed in order by Russia, Australia, Canada, the United States and Ghana.<ref name="Gold Production-2023" />
[[File:Gold 30g for a 860kg rock.jpg|thumb|left|Relative sizes of an {{cvt|860|kg|adj=on}} block of gold ore and the {{cvt|30|g|ozt}} of gold that can be extracted from it, Toi gold mine, Japan.]]

In South America, the controversial project Pascua Lama aims at exploitation of rich fields in the high mountains of Atacama Desert, at the border between Chile and Argentina.

It has been estimated that up to one-quarter of the yearly global gold production originates from artisanal or small scale mining.<ref>{{cite web |url=https://www.iisd.org/publications/global-trends-artisanal-and-small-scale-mining-asm-review-key-numbers-and-issues |last1=Fritz |first1=Morgane |last2=McQuilken |first2=James |last3=Collins |first3=Nina |last4=Weldegiorgis |first4=Fitsum |title=Global Trends in Artisanal and Small-Scale Mining (ASM): A review of key numbers and issues |via=Intergovernmental Forum on Mining, Minerals, Metals and Sustainable Development |format=PDF |type=Report |publisher=International Institute for Sustainable Development |location=Winnipeg Canada |date=January 2018 |access-date=24 February 2021}}</ref><ref>{{cite web |website=reuters.com |url=https://www.reuters.com/article/us-gold-mining-artisanal-explainer/what-is-artisanal-gold-and-why-is-it-booming-idUSKBN1ZE0YU |title=What is artisanal gold and why is it booming? |publisher=Reuters |date=15 January 2020 |access-date=24 February 2021 }}</ref><ref>{{Cite web |title=Removal of Barriers to the Abatement of Global Mercury Pollution from Artisanal Gold Mining |url=http://www.unido.org/fileadmin/import/10644_CHRISTIANtext.3.pdf |last=Beinhoff |first=Christian |access-date=29 December 2014 |url-status=dead |archive-url=https://web.archive.org/web/20160126032505/http://www.unido.org/fileadmin/import/10644_CHRISTIANtext.3.pdf |type=Report |archive-date=26 January 2016}}</ref>

The city of Johannesburg located in South Africa was founded as a result of the Witwatersrand Gold Rush which resulted in the discovery of some of the largest natural gold deposits in recorded history. The gold fields are confined to the northern and north-western edges of the Witwatersrand basin, which is a {{cvt|5|-|7|km|adj=on}} thick layer of archean rocks located, in most places, deep under the Free State, Gauteng and surrounding provinces.<ref name="Truswell-1977">Truswell, J.F. (1977). ''The Geological Evolution of South Africa''. pp. 21–28. Purnell, Cape Town. {{ISBN|9780360002906}}</ref> These Witwatersrand rocks are exposed at the surface on the Witwatersrand, in and around Johannesburg, but also in isolated patches to the south-east and south-west of Johannesburg, as well as in an arc around the Vredefort Dome which lies close to the center of the Witwatersrand basin.<ref name="McCarthy-2005" /><ref name="Truswell-1977" /> From these surface exposures the basin dips extensively, requiring some of the mining to occur at depths of nearly {{cvt|4000|m}}, making them, especially the Savuka and TauTona mines to the south-west of Johannesburg, the deepest mines on Earth. The gold is found only in six areas where archean rivers from the north and north-west formed extensive pebbly Braided river deltas before draining into the "Witwatersrand sea" where the rest of the Witwatersrand sediments were deposited.<ref name="Truswell-1977" />

The Second Boer War of 1899–1901 between the British Empire and the Afrikaner Boers was at least partly over the rights of miners and possession of the gold wealth in South Africa.

[[File:Kullanhuuhdontaa Ivalossa.jpg|thumb|Gold prospecting at the Ivalo River in the Finnish Lapland in 1898]]
During the 19th century, gold rushes occurred whenever large gold deposits were discovered. The first documented discovery of gold in the United States was at the Reed Gold Mine near Georgeville, North Carolina in 1803.<ref>{{cite web |url=http://www.nchistoricsites.org/Reed/reed.htm |archive-url=https://web.archive.org/web/20120115012324/http://www.nchistoricsites.org/Reed/reed.htm |url-status=dead |archive-date=15 January 2012 |title=Reed Gold Mine State Historic Site |last=Moore |first=Mark A. |date=2006 |publisher=North Carolina Office of Archives and History |access-date=13 December 2008}}</ref> The first major gold strike in the United States occurred in a small north Georgia town called Dahlonega.<ref>{{cite web |title=Road to adventure |publisher=Georgia Magazine |last=Garvey |first=Jane A. |url=http://www.georgiamagazine.org/archives_view.asp?mon=7&yr=2006&ID=1344 |date=2006 |access-date=23 January 2007 |url-status=dead |archive-url=https://web.archive.org/web/20070302212304/http://www.georgiamagazine.org/archives_view.asp?mon=7&yr=2006&ID=1344 |archive-date=2 March 2007 }}</ref> Further gold rushes occurred in California, Colorado, the Black Hills, Otago in New Zealand, a number of locations across Australia, Witwatersrand in South Africa, and the Klondike in Canada.

Grasberg mine located in Papua, Indonesia is the largest gold mine in the world.<ref>{{cite web|title=Grasberg Open Pit, Indonesia|url=http://www.mining-technology.com/projects/grasbergopenpit|website=Mining Technology|access-date=16 October 2017}}</ref>

=== Extraction and refining ===
{{Main|Gold extraction}}
[[File:Gold nuggets from Arizona.jpg|thumb|left|Gold Nuggets found in Arizona.]]
Gold extraction is most economical in large, easily mined deposits. Ore grades as little as 0.5 parts per million (ppm) can be economical. Typical ore grades in open-pit mines are 1–5 ppm; ore grades in underground or hard rock mines are usually at least 3 ppm. Because ore grades of 30 ppm are usually needed before gold is visible to the naked eye, in most gold mines the gold is invisible.

The average gold mining and extraction costs were about $317 per troy ounce in 2007, but these can vary widely depending on mining type and ore quality; global mine production amounted to 2,471.1 tonnes.<ref>{{Cite news |last=O'Connell |first=Rhona |date=13 April 2007 |title=Gold mine production costs up by 17% in 2006 while output fell |url=http://www.mineweb.net/mineweb/view/mineweb/en/page33?oid=19485&sn=Detail |url-status=dead |archive-url=https://web.archive.org/web/20141006084904/http://www.mineweb.net/mineweb/view/mineweb/en/page33?oid=19485&sn=Detail |archive-date=6 October 2014}}</ref>

After initial production, gold is often subsequently refined industrially by the Wohlwill process which is based on electrolysis or by the Miller process, that is chlorination in the melt. The Wohlwill process results in higher purity, but is more complex and is only applied in small-scale installations.<ref>{{Cite book |last=Noyes |first=Robert |url=https://books.google.com/books?id=__lqGczo9TwC&pg=PA342 |page=342 |title=Pollution prevention technology handbook |publisher=William Andrew |date=1993 |isbn=978-0-8155-1311-7}}</ref><ref>{{Cite book |last1=Pletcher |first1=Derek |first2=Frank |last2=Walsh |url=https://books.google.com/books?id=E_u9ARrm37oC&pg=PA244 |page=244 |title=Industrial electrochemistry |name-list-style=amp |publisher=Springer |date=1990 |isbn=978-0-412-30410-1}}</ref> Other methods of assaying and purifying smaller amounts of gold include parting and inquartation as well as cupellation, or refining methods based on the dissolution of gold in aqua regia.<ref>{{cite book |last1=Marczenko |first1=Zygmunt |last2=Balcerzak |first2=María |url=https://books.google.com/books?id=0NE1KjVISyAC&pg=PA210 |page=210 |title=Separation, preconcentration, and spectrophotometry in inorganic analysis |name-list-style=amp |publisher=Elsevier |date=2000 |isbn=978-0-444-50524-8}}</ref>

=== Recycling ===
In 1997, recycled gold accounted for approximately 20% of the 2700 tons of gold supplied to the market.<ref>{{cite book |doi=10.1002/14356007.a12_499 |chapter=Gold, Gold Alloys, and Gold Compounds |title=Ullmann's Encyclopedia of Industrial Chemistry |year=2000 |last1=Renner |first1=Hermann |last2=Schlamp |first2=Günther |last3=Hollmann |first3=Dieter |last4=Lüschow |first4=Hans Martin |last5=Tews |first5=Peter |last6=Rothaut |first6=Josef |last7=Dermann |first7=Klaus |last8=Knödler |first8=Alfons |last9=Hecht |first9=Christian |last10=Schlott |first10=Martin |last11=Drieselmann |first11=Ralf |last12=Peter |first12=Catrin |last13=Schiele |first13=Rainer |isbn=3-527-30673-0 }}</ref> Jewelry companies such as Generation Collection and computer companies including Dell conduct recycling.<ref>{{cite news|last=Paton|first=Elizabeth|date=23 April 2021|title=Does Recycled Gold Herald a Greener Future for Jewelry?|language=en-US|work=The New York Times|url=https://www.nytimes.com/2021/04/23/fashion/jewelry-recycled-gold.html |archive-url=https://ghostarchive.org/archive/20211228/https://www.nytimes.com/2021/04/23/fashion/jewelry-recycled-gold.html |archive-date=28 December 2021 |url-access=limited|access-date=17 May 2021|issn=0362-4331}}{{cbignore}}</ref>

As of 2020, the amount of carbon dioxide {{chem2|CO2}} produced in mining a kilogram of gold is 16 tonnes, while recycling a kilogram of gold produces 53 kilograms of {{chem2|CO2}} equivalent. Approximately 30 percent of the global gold supply is recycled and not mined as of 2020.<ref>{{cite news |last=Baraniuk |first=Chris |title=Why it's getting harder to mine gold |url=https://www.bbc.com/future/article/20201026-why-its-getting-harder-to-mine-gold |publisher=BBC |date=27 October 2020 |access-date=29 October 2020}}</ref>

=== Consumption ===
{{update|date=May 2022}}
{| style=" text-align:right;float:right" class="wikitable sortable"
|+ Gold jewelry consumption by country (in tonnes)<ref>{{cite news |url=http://www.forexyard.com/en/news/Gold-jewellery-consumption-by-country-2011-02-28T130619Z-FACTBOX |archive-url=https://web.archive.org/web/20120112003914/http://www.forexyard.com/en/news/Gold-jewellery-consumption-by-country-2011-02-28T130619Z-FACTBOX |archive-date=12 January 2012 |title=Gold jewellery consumption by country |date=28 February 2011 |agency=Reuters}}</ref><ref>{{cite web |url=http://www.gold.org/investment/research/regular_reports/gold_demand_trends/ |title=Gold Demand Trends |date=12 November 2015}}</ref>
|-
! Country !! 2009 !! 2010 !! 2011 !! 2012 !! 2013
|-
| align=left|{{flag|India}} || 442.37 || 745.70 || 986.3 || 864 || 974
|-
| align=left|{{flag|China}} || 376.96 || 428.00 || 921.5 || 817.5 || 1120.1
|-
| align=left|{{flag|United States}} || 150.28 || 128.61 || 199.5 || 161 || 190
|-
| align=left|{{flag|Turkey}} || 75.16 || 74.07 || 143 || 118 || 175.2
|-
| align=left|{{flag|Saudi Arabia}} || 77.75 || 72.95 || 69.1 ||58.5 || 72.2
|-
| align=left|{{flag|Russia}} || 60.12 || 67.50 || 76.7 || 81.9 || 73.3
|-
| align=left|{{flag|United Arab Emirates}} || 67.60 || 63.37 || 60.9 ||58.1 || 77.1
|-
| align=left|{{flag|Egypt}} || 56.68 || 53.43 || 36 ||47.8 || 57.3
|-
| align=left|{{flag|Indonesia}} || 41.00 || 32.75 || 55 || 52.3 || 68
|-
| align=left|{{flag|United Kingdom}} || 31.75 || 27.35 || 22.6 || 21.1 || 23.4
|-
| align=left|Other Persian Gulf Countries || 24.10 || 21.97 || 22 || 19.9 || 24.6
|-
| align=left|{{flag|Japan}} || 21.85 || 18.50 || −30.1 || 7.6 || 21.3
|-
| align=left|{{flag|South Korea}} || 18.83 || 15.87 || 15.5 ||12.1 || 17.5
|-
| align=left|{{flag|Vietnam}} || 15.08 || 14.36 || 100.8 || 77 || 92.2
|-
| align=left|{{flag|Thailand}} || 7.33 || 6.28 || 107.4 || 80.9 || 140.1
|-
| align=left|'''Total''' || '''1466.86''' || '''1770.71''' || '''2786.12 ''' || '''2477.7''' || '''3126.1 '''
|-
| align=left|''Other Countries'' || ''251.6'' || ''254.0'' || ''390.4'' || ''393.5'' || ''450.7''
|-
| align=left|'''World Total''' || '''1718.46''' || '''2024.71''' || '''3176.52'''|| '''2871.2''' || '''3576.8'''
|}
The consumption of gold produced in the world is about 50% in jewelry, 40% in investments, and 10% in industry.<ref name="Soos-2011" /><ref>{{cite web |url=http://www.usdebtclock.org/gold-demand-by-country.html |title=Country wise gold demand |access-date=2 October 2015}}</ref>

According to the World Gold Council, China was the world's largest single consumer of gold in 2013, overtaking India.<ref>{{cite web |last=Harjani |first=Ansuya |url=https://www.cnbc.com/2014/02/18/its-official-china-overtakes-india-as-top-consumer-of-gold.html |title=It's official: China overtakes India as top consumer of gold |publisher=CNBC |date=18 February 2014 |access-date=2 July 2014}}</ref>

=== Pollution ===
{{further|Mercury cycle|International Cyanide Management Code}}
Gold production is associated with contribution to hazardous pollution.<ref>{{cite journal |last2=Marikar |first2=Fouzul |last1=Abdul-Wahab |title=The environmental impact of gold mines: pollution by heavy metals |journal=Central European Journal of Engineering |volume=2 |issue=2 |pages=304–313 |date=24 October 2011 |bibcode=2012CEJE....2..304A|s2cid=3916088 |doi=10.2478/s13531-011-0052-3|doi-access=free }}</ref>

Low-grade gold ore may contain less than one ppm gold metal; such ore is ground and mixed with sodium cyanide to dissolve the gold. Cyanide is a highly poisonous chemical, which can kill living creatures when exposed in minute quantities. Many cyanide spills<ref>[http://www.deseretnews.com/article/810435/Cyanide-spill-compared-to-Chernobyls---N-disaster.html Cyanide spills from gold mine compared to Chernobyl's nuclear disaster] {{webarchive |url=https://web.archive.org/web/20180714135300/https://www.deseretnews.com/article/810435/Cyanide-spill-compared-to-Chernobyls---N-disaster.html |date=14 July 2018}}. Deseretnews.com (14 February 2000). Retrieved on 4 May 2012.</ref> from gold mines have occurred in both developed and developing countries which killed aquatic life in long stretches of affected rivers. Environmentalists consider these events major environmental disasters.<ref>[http://news.bbc.co.uk/2/hi/europe/642880.stm Death of a river] {{Webarchive|url=https://web.archive.org/web/20090109134649/http://news.bbc.co.uk/2/hi/europe/642880.stm |date=9 January 2009 }}. BBC News (15 February 2000). Retrieved on 4 May 2012.</ref><ref>[http://www.abc.net.au/am/stories/s98890.htm Cyanide spill second only to Chernobyl] {{Webarchive|url=https://web.archive.org/web/20170525072149/http://www.abc.net.au/am/stories/s98890.htm |date=25 May 2017 }}. Abc.net.au. 11 February 2000. Retrieved on 4 May 2012.</ref> Up to thirty tons of used ore can be dumped as waste for producing one troy ounce of gold.<ref name="NYT-2005">[https://www.nytimes.com/2005/10/24/international/24GOLD.html Behind gold's glitter, torn lands and pointed questions] {{Webarchive|url=https://web.archive.org/web/20150408113857/http://www.nytimes.com/2005/10/24/international/24GOLD.html |date=8 April 2015 }}, ''The New York Times'', 24 October 2005</ref> Gold ore dumps are the source of many heavy elements such as cadmium, lead, zinc, copper, arsenic, selenium and mercury. When sulfide-bearing minerals in these ore dumps are exposed to air and water, the sulfide transforms into sulfuric acid which in turn dissolves these heavy metals facilitating their passage into surface water and ground water. This process is called acid mine drainage. These gold ore dumps contain long-term, highly hazardous waste.<ref name="NYT-2005" />

It was once common to use mercury to recover gold from ore, but today the use of mercury is largely limited to small-scale individual miners.<ref>{{cite web |url=http://www.worstpolluted.org/files/FileUpload/files/WWPP_2012.pdf |archive-url=https://web.archive.org/web/20150402130613/http://www.worstpolluted.org/files/FileUpload/files/WWPP_2012.pdf |archive-date=2 April 2015 |url-status=live |title=Pollution from Artisanal Gold Mining, Blacksmith Institute Report 2012 |access-date=22 September 2015}}</ref> Minute quantities of mercury compounds can reach water bodies, causing heavy metal contamination. Mercury can then enter into the human food chain in the form of methylmercury. Mercury poisoning in humans can cause severe brain damage.<ref>{{cite web|last=Wroblewski|first=William|date=12 January 2022|title='Babies here are born sick': are Bolivia's gold mines poisoning its indigenous people?|url=https://www.theguardian.com/global-development/2022/jan/12/babies-here-are-born-sick-are-bolivias-gold-mines-poisoning-its-indigenous-people|access-date=12 January 2022|website=The Guardian|language=en}}</ref>

Gold extraction is also a highly energy-intensive industry, extracting ore from deep mines and grinding the large quantity of ore for further chemical extraction requires nearly 25 kWh of electricity per gram of gold produced.<ref>{{cite journal |doi=10.1016/j.jclepro.2012.01.042 |title=Using life cycle assessment to evaluate some environmental impacts of gold |date=2012 |last1=Norgate |first1=Terry |last2=Haque |first2=Nawshad |journal=Journal of Cleaner Production |volume=29–30 |pages=53–63}}</ref>

== Monetary use ==
{{Further|History of money}}
[[File:Two 20kr gold coins.png|thumb|right|Two golden 20 kr coins from the Scandinavian Monetary Union, which was based on a gold standard. The coin to the left is Swedish and the right one is Danish.]]
Gold has been widely used throughout the world as money,<ref>{{Cite book |url=https://books.google.com/books?id=Hx-AU99lho4C&pg=PA192 |title=Man, Economy, and State, Scholar's Edition |last=Rothbard |first=Murray N. |date=2009 |publisher=Ludwig von Mises Institute |isbn=978-1-933550-99-2}}</ref> for efficient indirect exchange (versus barter), and to store wealth in hoards. For exchange purposes, mints produce standardized gold bullion coins, bars and other units of fixed weight and purity.

The first known coins containing gold were struck in Lydia, Asia Minor, around 600 BC.<ref name="Lion-2003">{{cite web |url=http://rg.ancients.info/lion/article.html |title=A Case for the World's Oldest Coin: Lydian Lion |publisher=Rg.ancients.info |date=2 October 2003 |access-date=27 October 2013 |archive-date=13 October 2018 |archive-url=https://web.archive.org/web/20181013171219/http://rg.ancients.info/lion/article.html |url-status=dead }}</ref> The ''talent'' coin of gold in use during the periods of Grecian history both before and during the time of the life of Homer weighed between 8.42 and 8.75 grams.<ref>{{cite book |last=Seltman |first=C. T. |url=https://books.google.com/books?id=Uas8AAAAIAAJ&pg=PA116 |title=Athens, Its History and Coinage Before the Persian Invasion |access-date=4 June 2012 |isbn=978-0-87184-308-1 |date=1924}}</ref> From an earlier preference in using silver, European economies re-established the minting of gold as coinage during the thirteenth and fourteenth centuries.<ref name="Postan-1967">{{cite book |last1=Postan |first1=M. M. |last2=Miller |first2=E. |url=https://books.google.com/books?id=wSia_4PpeqQC&pg=PR1 |title=The Cambridge Economic History of Europe: Trade and industry in the Middle Ages |publisher=Cambridge University Press, 28 August 1987 |isbn=978-0-521-08709-4 |date=1967}}</ref>

Bills (that mature into gold coin) and gold certificates (convertible into gold coin at the issuing bank) added to the circulating stock of gold standard money in most 19th century industrial economies. In preparation for World War I the warring nations moved to fractional gold standards, inflating their currencies to finance the war effort. Post-war, the victorious countries, most notably Britain, gradually restored gold-convertibility, but international flows of gold via bills of exchange remained embargoed; international shipments were made exclusively for bilateral trades or to pay war reparations.

After World War II gold was replaced by a system of nominally convertible currencies related by fixed exchange rates following the Bretton Woods system. Gold standards and the direct convertibility of currencies to gold have been abandoned by world governments, led in 1971 by the United States' refusal to redeem its dollars in gold. Fiat currency now fills most monetary roles. Switzerland was the last country to tie its currency to gold; this was ended by a referendum in 1999.<ref>{{cite news |url=https://www.nytimes.com/1999/04/19/world/swiss-narrowly-vote-to-drop-gold-standard.html |work=The New York Times |title=Swiss Narrowly Vote to Drop Gold Standard |date=19 April 1999 |access-date=1 July 2022}}</ref>

[[File:Goldvault nyc.jpg|thumb|left|A gold vault at the Federal Reserve Bank of New York]]
Central banks continue to keep a portion of their liquid reserves as gold in some form, and metals exchanges such as the London Bullion Market Association still clear transactions denominated in gold, including future delivery contracts. Today, gold mining output is declining.<ref>{{cite web |last=King |first=Byron |url=http://goldnews.bullionvault.com/gold_mine_production_072020092 |archive-url=http://arquivo.pt/wayback/20160515213855/http://goldnews.bullionvault.com/gold_mine_production_072020092 |archive-date=15 May 2016 |title=Gold mining decline |publisher=BullionVault.com |date=20 July 2009 |access-date=23 November 2009}}</ref> With the sharp growth of economies in the 20th century, and increasing foreign exchange, the world's gold reserves and their trading market have become a small fraction of all markets and fixed exchange rates of currencies to gold have been replaced by floating prices for gold and gold future contract. Though the gold stock grows by only 1% or 2% per year, very little metal is irretrievably consumed. Inventory above ground would satisfy many decades of industrial and even artisan uses at current prices.

The gold proportion (fineness) of alloys is measured by karat (k). Pure gold (commercially termed ''fine'' gold) is designated as 24 karat, abbreviated 24k. English gold coins intended for circulation from 1526 into the 1930s were typically a standard 22k alloy called crown gold,<ref>{{cite book |last1=Lawrence |first1=Thomas Edward |url=https://books.google.com/books?id=tu86AAAAIAAJ&pg=PA103 |page=103 |title=The Mint: A Day-book of the R.A.F. Depot Between August and December 1922, with Later Notes |date=1948}}</ref> for hardness (American gold coins for circulation after 1837 contain an alloy of 0.900 fine gold, or 21.6 kt).<ref>{{cite book |last=Tucker |first=George |url=https://archive.org/details/theorymoneyandb00tuckgoog |title=The theory of money and banks investigated |publisher=C. C. Little and J. Brown |date=1839}}</ref>

Although the prices of some platinum group metals can be much higher, gold has long been considered the most desirable of precious metals, and its value has been used as the standard for many currencies. Gold has been used as a symbol for purity, value, royalty, and particularly roles that combine these properties. Gold as a sign of wealth and prestige was ridiculed by Thomas More in his treatise ''Utopia''. On that imaginary island, gold is so abundant that it is used to make chains for slaves, tableware, and lavatory seats. When ambassadors from other countries arrive, dressed in ostentatious gold jewels and badges, the Utopians mistake them for menial servants, paying homage instead to the most modestly dressed of their party.

The ISO 4217 currency code of gold is XAU.<ref>{{cite web |url=http://www.iso.org/iso/home/standards/currency_codes.htm |title=Currency codes – ISO 4217 |publisher=International Organization for Standardization |access-date=25 December 2014}}</ref> Many holders of gold store it in form of bullion coins or bars as a hedge against inflation or other economic disruptions, though its efficacy as such has been questioned; historically, it has not proven itself reliable as a hedging instrument.<ref>{{Cite web |url=https://medium.com/hedgehound/hedgehound-fridayfinance-on-hedging-inflation-with-gold-375f3ce09cfe |title=On hedging inflation with gold |last=Valenta |first=Philip |date=22 June 2018 |website=Medium|access-date=30 November 2018}}</ref> Modern bullion coins for investment or collector purposes do not require good mechanical wear properties; they are typically fine gold at 24k, although the American Gold Eagle and the British gold sovereign continue to be minted in 22k (0.92) metal in historical tradition, and the South African Krugerrand, first released in 1967, is also 22k (0.92).<ref>{{cite web |url=http://www.americansilvereagletoday.com/the-ever-popular-krugerrand |archive-url=https://web.archive.org/web/20110203024339/http://www.americansilvereagletoday.com/the-ever-popular-krugerrand/ |archive-date=3 February 2011 |title=The Ever Popular Krugerrand |date=2010 |website=americansilvereagletoday.com |access-date=30 August 2011}}</ref>

The ''special issue'' Canadian Gold Maple Leaf coin contains the highest purity gold of any bullion coin, at 99.999% or 0.99999, while the ''popular issue'' Canadian Gold Maple Leaf coin has a purity of 99.99%. In 2006, the United States Mint began producing the American Buffalo gold bullion coin with a purity of 99.99%. The Australian Gold Kangaroos were first coined in 1986 as the Australian Gold Nugget but changed the reverse design in 1989. Other modern coins include the Austrian Vienna Philharmonic bullion coin and the Chinese Gold Panda.<ref>{{cite web |url=https://goldsilver.com/blog/what-are-the-different-purities-of-sovereign-gold-coins/ |title=What Are the Different Purities of Sovereign Gold Coins? |website=goldsilver.com |access-date=29 March 2021}}</ref>

=== Price ===
{{further|Gold as an investment}}
[[File:Gold price in USD.png|thumb|upright=1.35|Gold price history in 1960–present.]]

Like other precious metals, gold is measured by troy weight and by grams. The proportion of gold in the alloy is measured by ''karat'' (k), with 24 karat (24k) being pure gold (100%), and lower karat numbers proportionally less (18k = 75%). The purity of a gold bar or coin can also be expressed as a decimal figure ranging from 0 to 1, known as the millesimal fineness, such as 0.995 being nearly pure.

The price of gold is determined through trading in the gold and derivatives markets, but a procedure known as the Gold Fixing in London, originating in September 1919, provides a daily benchmark price to the industry. The afternoon fixing was introduced in 1968 to provide a price when US markets are open.<ref>{{cite book |last1=Warwick-Ching |first1=Tony |url=https://books.google.com/books?id=GrQQxVrtJ3sC&pg=PA26 |page=26 |title=The International Gold Trade |isbn=978-1-85573-072-4 |date=28 February 1993|publisher=Woodhead }}</ref> {{as of|2025|April|}}, gold was valued at around $106 per gram ($3,300 per troy ounce).

==== History ====
Historically gold coinage was widely used as currency; when paper money was introduced, it typically was a receipt redeemable for gold coin or bullion. In a monetary system known as the gold standard, a certain weight of gold was given the name of a unit of currency. For a long period, the United States government set the value of the US dollar so that one troy ounce was equal to $20.67 ($0.665 per gram), but in 1934 the dollar was devalued to $35.00 per troy ounce ($0.889/g). By 1961, it was becoming hard to maintain this price, and a pool of US and European banks agreed to manipulate the market to prevent further currency devaluation against increased gold demand.<ref>{{cite book |last1=Elwell |url=https://books.google.com/books?id=ztHyT2ew3QUC&pg=PA11 |pages=11–13 |title=Brief History of the Gold Standard (GS) in the United States |isbn=978-1-4379-8889-5 |first1=Craig K. |date=2011| publisher=DIANE }}</ref>

The largest gold depository in the world is that of the U.S. Federal Reserve Bank in New York, which holds about 3%<ref name="Hitzer-2006">{{cite web |first2=Christian |last2=Perwass |url=http://sinai.apphy.u-fukui.ac.jp/gcj/publications/gold/gold.pdf |archive-url=https://web.archive.org/web/20120127152357/http://sinai.apphy.u-fukui.ac.jp/gcj/publications/gold/gold.pdf |archive-date=27 January 2012 |title=The hidden beauty of gold |access-date=10 May 2011 |last1=Hitzer |first1=Eckhard |date=22 November 2006 |website=Proceedings of the International Symposium on Advanced Mechanical and Power Engineering 2007 (ISAMPE 2007) between Pukyong National University (Korea), University of Fukui (Japan) and University of Shanghai for Science and Technology (China), 22–25 November 2006, hosted by the University of Fukui (Japan), pp. 157–167. (Figs 15,16,17,23 revised.)}}</ref> of the gold known to exist and accounted for today, as does the similarly laden U.S. Bullion Depository at Fort Knox. In 2005 the World Gold Council estimated total global gold supply to be 3,859 tonnes and demand to be 3,754 tonnes, giving a surplus of 105 tonnes.<ref>{{cite web |url=http://www.gold.org/value/stats/statistics/gold_demand/index.html |archive-url=https://web.archive.org/web/20060719111349/http://www.gold.org/value/stats/statistics/gold_demand/index.html |archive-date=19 July 2006 |title=World Gold Council > value > research & statistics > statistics > supply and demand statistics |access-date=22 July 2006}}</ref>

After 15 August 1971 Nixon shock, the price began to greatly increase,<ref>{{cite web |publisher=kitco |url=http://www.kitco.com/charts/historicalgold.html |title=historical charts:gold – 1833–1999 yearly averages |access-date=30 June 2012}}</ref> and between 1968 and 2000 the price of gold ranged widely, from a high of $850 per troy ounce ($27.33/g) on 21 January 1980, to a low of $252.90 per troy ounce ($8.13/g) on 21 June 1999 (London Gold Fixing).<ref>[http://kitco.com/LFgif/au75-pres.gif Kitco.com] {{Webarchive|url=https://web.archive.org/web/20180714081628/http://www.kitco.com/LFgif/au75-pres.gif |date=14 July 2018 }}, Gold – London PM Fix 1975 – present (GIF), Retrieved 22 July 2006.</ref> Prices increased rapidly from 2001, but the 1980 high was not exceeded until 3 January 2008, when a new maximum of $865.35 per troy ounce was set.<ref name="Lbma-2008">{{cite web |url=http://www.lbma.org.uk/2008dailygold.htm |archive-url=https://web.archive.org/web/20090210035134/http://lbma.org.uk/2008dailygold.htm |archive-date=10 February 2009 |title=LBMA statistics |publisher=Lbma.org.uk |date=31 December 2008 |access-date=5 April 2009}}</ref> Another record price was set on 17 March 2008, at $1023.50 per troy ounce ($32.91/g).<ref name="Lbma-2008" />

On 2 December 2009, gold reached a new high closing at $1,217.23.<ref>{{cite news |url=http://news.bbc.co.uk/2/hi/business/8390779.stm |title=Gold hits yet another record high |work=BBC News |date=2 December 2009 |access-date=6 December 2009}}</ref> Gold further rallied hitting new highs in May 2010 after the European Union debt crisis prompted further purchase of gold as a safe asset.<ref>{{Cite news |title=PRECIOUS METALS: Comex Gold Hits All-Time High |newspaper=The Wall Street Journal |date=11 May 2012 |url=https://www.wsj.com/article/BT-CO-20100511-717954.html |access-date=4 August 2010}} {{dead link|date=June 2016|bot=medic}}{{cbignore|bot=medic}}</ref><ref>{{cite web |url=http://www.marketwatch.com/story/gold-prices-resume-rise-as-eu-plan-pondered-2010-05-11 |title=Gold futures hit closing record as investors fret rescue deal |last1=Gibson |first1=Kate |last2=Chang |first2=Sue |date=11 May 2010 |website=MarketWatch |access-date=4 August 2010}}</ref> On 1 March 2011, gold hit a new all-time high of $1432.57, based on investor concerns regarding ongoing unrest in North Africa as well as in the Middle East.<ref>{{cite news |url=https://www.reuters.com/article/markets-global-idUSN0115419520110301 |title=Gold hits record, oil jumps with Libya unrest |work=Reuters |date=1 March 2011 |access-date=1 March 2011 |first=Caroline |last=Valetkevitch |archive-date=15 October 2015 |archive-url=https://web.archive.org/web/20151015231151/http://www.reuters.com/article/2011/03/01/markets-global-idUSN0115419520110301 |url-status=live }}</ref>

From April 2001 to August 2011, spot gold prices more than quintupled in value against the US dollar, hitting a new all-time high of $1,913.50 on 23 August 2011,<ref>{{cite news |url=https://www.bloomberg.com/news/2011-08-25/cash-gold-may-advance-after-dropping-most-in-18-months-as-shares-rebound.html |title=Gold Extends Biggest Decline in 18 Months After CME Raises Futures Margins |publisher=Bloomberg |date=23 August 2011 |access-date=24 February 2021 |first=Glenys |last=Sim |url-status=live |archive-url=https://web.archive.org/web/20140110002029/http://www.bloomberg.com/news/2011-08-25/cash-gold-may-advance-after-dropping-most-in-18-months-as-shares-rebound.html |archive-date=10 January 2014}}</ref> prompting speculation that the long secular bear market had ended and a bull market had returned.<ref>{{cite web |url=http://www.ameinfo.com/75511.html |archive-url=https://web.archive.org/web/20090421094351/http://www.ameinfo.com/75511.html |archive-date=21 April 2009 |title=Financial Planning{{!}}Gold starts 2006 well, but this is not a 25-year high! |publisher=Ameinfo.com|access-date=5 April 2009}}</ref> However, the price then began a slow decline towards $1200 per troy ounce in late 2014 and 2015.

In August 2020, the gold price picked up to US$2060 per ounce after a total growth of 59% from August 2018 to October 2020, a period during which it outplaced the Nasdaq total return of 54%.<ref>{{cite web|url=https://www.efgbank.com/it/coronavirus/14-October-2020.html|date=14 October 2020 |title=Gold, monetary policy and the US dollar|first=GianLuigi |last=Mandruzzato|url-status=dead|archive-url=https://web.archive.org/web/20201106083115/https://www.efgbank.com/it/coronavirus/14-October-2020.html|archive-date=6 November 2020 }}</ref>

Gold futures are traded on the COMEX exchange.<ref name="PortaraCQG">{{Cite web |title=Historical Gold Intraday Futures Data (GCA) |url=https://portaracqg.com/historical-futures-data/gold-intraday-data-gca/ |access-date=28 April 2022 |website=PortaraCQG |language=en-US}}</ref> These contacts are priced in USD per troy ounce (1 troy ounce = 31.1034768 grams).<ref>{{Cite web |title=Troy Ounce |url=https://www.investopedia.com/terms/t/troyounce.asp |access-date=28 April 2022 |website=Investopedia |language=en}}</ref> Below are the CQG contract specifications outlining the futures contracts:
{| class="wikitable"
|+Contract Specifications<ref name="PortaraCQG" />
!Gold (GCA)
!
|-
|Exchange:
|COMEX
|-
|Sector:
|Metal
|-
|Tick Size:
|0.1
|-
|Tick Value:
|10 USD
|-
|BPV:
|100
|-
|Denomination:
|USD
|-
|Decimal Place:
|1
|}

== Other applications ==
=== Jewelry ===
[[File:MocheGoldNecklace.jpg|thumb|Moche gold necklace depicting feline heads. Larco Museum Collection, Lima, Peru.]]
[[File:Boule de Genève, ca. 1890.jpeg|thumb|A 21.5k yellow gold pendant watch so-called "Boule de Genève" (Geneva ball), {{Circa|1890}}.]]
Because of the softness of pure (24k) gold, it is usually alloyed with other metals for use in jewelry, altering its hardness and ductility, melting point, color and other properties. Alloys with lower karat rating, typically 22k, 18k, 14k or 10k, contain higher percentages of copper, silver, palladium or other base metals in the alloy.<ref name="WorldGoldCouncil">[https://web.archive.org/web/20080619061619/http://www.utilisegold.com/jewellery_technology/colours/colour_alloys/ Jewellery Alloys]. World Gold Council</ref> Nickel is toxic, and its release from nickel white gold is controlled by legislation in Europe.<ref name="WorldGoldCouncil" /> Palladium-gold alloys are more expensive than those using nickel.<ref>{{Cite book |url=https://books.google.com/books?id=W_hTAAAAMAAJ |title=Professional goldsmithing: a contemporary guide to traditional jewelry techniques |last=Revere |first=Alan |date=1 May 1991 |publisher=Van Nostrand Reinhold |isbn=978-0-442-23898-8}}</ref> High-karat white gold alloys are more resistant to corrosion than are either pure silver or sterling silver. The Japanese craft of Mokume-gane exploits the color contrasts between laminated colored gold alloys to produce decorative wood-grain effects.

By 2014, the gold jewelry industry was escalating despite a dip in gold prices. Demand in the first quarter of 2014 pushed turnover to $23.7 billion according to a World Gold Council report.

Gold solder is used for joining the components of gold jewelry by high-temperature hard soldering or brazing. If the work is to be of hallmarking quality, the gold solder alloy must match the fineness of the work, and alloy formulas are manufactured to color-match yellow and white gold. Gold solder is usually made in at least three melting-point ranges referred to as Easy, Medium and Hard. By using the hard, high-melting point solder first, followed by solders with progressively lower melting points, goldsmiths can assemble complex items with several separate soldered joints. Gold can also be made into thread and used in embroidery.

=== Electronics ===
Only 10% of the world consumption of new gold produced goes to industry,<ref name="Soos-2011" /> but by far the most important industrial use for new gold is in fabrication of corrosion-free electrical connectors in computers and other electrical devices. For example, according to the World Gold Council, a typical cell phone may contain 50 mg of gold, worth about three dollars. But since nearly one billion cell phones are produced each year, a gold value of US$2.82 in each phone adds to US$2.82 billion in gold from just this application.<ref>[http://www.usfunds.com/slideshows/the-many-uses-of-gold/ Uses of gold] {{Webarchive|url=https://archive.today/20141104233515/http://www.usfunds.com/slideshows/the-many-uses-of-gold/ |date=4 November 2014 }} Accessed 4 November 2014</ref> (Prices updated to November 2022)

Though gold is attacked by free chlorine, its good conductivity and general resistance to oxidation and corrosion in other environments (including resistance to non-chlorinated acids) has led to its widespread industrial use in the electronic era as a thin-layer coating on electrical connectors, thereby ensuring good connection. For example, gold is used in the connectors of the more expensive electronics cables, such as audio, video and USB cables. The benefit of using gold over other connector metals such as tin in these applications has been debated; gold connectors are often criticized by audio-visual experts as unnecessary for most consumers and seen as simply a marketing ploy. However, the use of gold in other applications in electronic sliding contacts in highly humid or corrosive atmospheres, and in use for contacts with a very high failure cost (certain computers, communications equipment, spacecraft, jet aircraft engines) remains very common.<ref>{{cite book |editor-last=Krech III |editor-first=Shepard |editor2-last=Merchant |editor2-first=Carolyn |editor3-last=McNeill |editor3-first=John Robert |title=Encyclopedia of World Environmental History |volume=2: F–N |year=2004 |publisher=Routledge |isbn=978-0-415-93734-4 |pages=597– |url={{google books |plainurl=y |id=G7JrhAy5phoC |page=597}} }}</ref>

Besides sliding electrical contacts, gold is also used in electrical contacts because of its resistance to corrosion, electrical conductivity, ductility and lack of toxicity.<ref>{{cite web |title=General Electric Contact Materials |website=Electrical Contact Catalog (Material Catalog) |publisher=Tanaka Precious Metals |date=2005 |url=http://www.tanaka-precious.com/catalog/material.html|archive-url=https://web.archive.org/web/20010303213152/http://www.tanaka-precious.com/catalog/material.html|url-status=dead|archive-date=3 March 2001 |access-date=21 February 2007}}</ref> Switch contacts are generally subjected to more intense corrosion stress than are sliding contacts. Fine gold wires are used to connect semiconductor devices to their packages through a process known as wire bonding.

The concentration of free electrons in gold metal is 5.91×1022 cm−3.<ref>{{Cite book |url=https://books.google.com/books?id=MaWKDQAAQBAJ&pg=SA2-PA8 |title=Electronic, Magnetic, and Optical Materials, Second Edition |last1=Fulay |first1=Pradeep |last2=Lee |first2=Jung-Kun |date=2016 |publisher=CRC Press |isbn=978-1-4987-0173-0}}</ref> Gold is highly conductive to electricity and has been used for electrical wiring in some high-energy applications (only silver and copper are more conductive per volume, but gold has the advantage of corrosion resistance). For example, gold electrical wires were used during some of the Manhattan Project's atomic experiments, but large high-current silver wires were used in the calutron isotope separator magnets in the project.

It is estimated that 16% of the world's presently-accounted-for gold and 22% of the world's silver is contained in electronic technology in Japan.<ref>{{cite news |url=http://www.techradar.com/news/phone-and-communications/mobile-phones/japan-wants-citizens-to-donate-their-phone-to-make-2020-olympic-medals-1326938 |title=Japan wants citizens to donate their old phone to make 2020 Olympics medals |work=TechRadar |date=23 August 2016 |author=Peckham, James}}</ref>

=== Medicine ===
There are only two gold compounds currently employed as pharmaceuticals in modern medicine (sodium aurothiomalate and auranofin), used in the treatment of arthritis and other similar conditions in the US due to their anti-inflammatory properties. These drugs have been explored as a means to help to reduce the pain and swelling of rheumatoid arthritis, and also (historically) against tuberculosis and some parasites.<ref name="Messori-2004">{{Cite book |first1=L. |last1=Messori |first2=G. |last2=Marcon |chapter-url=https://books.google.com/books?id=wgifUs8dFbgC&pg=PA279 |chapter=Gold Complexes in the treatment of Rheumatoid Arthritis |title=Metal ions and their complexes in medication |editor-last=Sigel |editor-first=Astrid |publisher=CRC Press |date=2004 |isbn=978-0-8247-5351-1 |pages=280–301}}</ref><ref name = mech08>{{cite journal | vauthors = Kean WF, Kean IR | title = Clinical pharmacology of gold | journal = Inflammopharmacology | volume = 16 | issue = 3 | pages = 112–25 | date = June 2008 | pmid = 18523733 | doi = 10.1007/s10787-007-0021-x | s2cid = 808858 }}</ref>

Some esotericists and forms of alternative medicine assign metallic gold a healing power, against the scientific consensus{{Citation Needed|date=January 2025}}.

Historically, metallic and gold compounds have long been used for medicinal purposes. Gold, usually as the metal, is perhaps the most anciently administered medicine (apparently by shamanic practitioners)<ref name=mech08 /> and known to Dioscorides.<ref>{{cite book |last1=Moir |first1=David Macbeth |url=https://archive.org/details/b21364047 |page=[https://archive.org/details/b21364047/page/225 225] |title=Outlines of the ancient history of medicine |publisher=William Blackwood |date=1831}}</ref><ref>Mortier, Tom. [https://lirias.kuleuven.be/bitstream/1979/254/2/thesis_finaal.pdf An experimental study on the preparation of gold nanoparticles and their properties] {{Webarchive|url=https://web.archive.org/web/20131005015930/https://lirias.kuleuven.be/bitstream/1979/254/2/thesis_finaal.pdf |date=5 October 2013 }}, PhD thesis, University of Leuven (May 2006)</ref> In medieval times, gold was often seen as beneficial for the health, in the belief that something so rare and beautiful could not be anything but healthy.

In the 19th century gold had a reputation as an anxiolytic, a therapy for nervous disorders. Depression, epilepsy, migraine, and glandular problems such as amenorrhea and impotence were treated, and most notably alcoholism (Keeley, 1897).<ref>{{Cite journal |last1=Richards |first1=Douglas G. |last2=McMillin |first2=David L. |last3=Mein |first3=Eric A. |last4=Nelson |first4=Carl D. |name-list-style=amp |title=Gold and its relationship to neurological/glandular conditions |journal=The International Journal of Neuroscience |volume=112 |issue=1 |pages=31–53 |date=January 2002 |pmid=12152404 |doi=10.1080/00207450212018|s2cid=41188687 }}</ref>

The apparent paradox{{Explain|date=January 2025|reason=What paradox?}} of the actual toxicology of the substance suggests the possibility of serious gaps in the understanding of the action of gold in physiology.<ref>{{cite journal |doi=10.1006/biol.1997.0123 |pmid=9637749 |title=Gold, the Noble Metal and the Paradoxes of its Toxicology |date=1998 |last1=Merchant |first1=B. |journal=Biologicals |volume=26 |pages=49–59 |issue=1}}</ref> Only salts and radioisotopes of gold are of pharmacological value, since elemental (metallic) gold is inert to all chemicals it encounters inside the body (e.g., ingested gold cannot be attacked by stomach acid).

[[File:Gold255.jpg|thumb|Colloidal gold varies in color with the size of gold particles]]
Gold alloys are used in restorative dentistry, especially in tooth restorations, such as crowns and permanent bridges. The gold alloys' slight malleability facilitates the creation of a superior molar mating surface with other teeth and produces results that are generally more satisfactory than those produced by the creation of porcelain crowns. The use of gold crowns in more prominent teeth such as incisors is favored in some cultures and discouraged in others.

Colloidal gold preparations (suspensions of gold nanoparticles) in water are intensely red-colored, and can be made with tightly controlled particle sizes up to a few tens of nanometers across by reduction of gold chloride with citrate or ascorbate ions. Colloidal gold is used in research applications in medicine, biology and materials science. The technique of immunogold labeling exploits the ability of the gold particles to adsorb protein molecules onto their surfaces. Colloidal gold particles coated with specific antibodies can be used as probes for the presence and position of antigens on the surfaces of cells.<ref>{{Cite journal |doi=10.1016/0019-2791(71)90496-4 |pmid=4110101 |date=1971 |last1=Faulk |first1=W. P. |last2=Taylor |first2=G. M. |title=An immunocolloid method for the electron microscope |volume=8 |issue=11 |pages=1081–3 |journal=Immunochemistry}}</ref> In ultrathin sections of tissues viewed by electron microscopy, the immunogold labels appear as extremely dense round spots at the position of the antigen.<ref>{{Cite journal |pmid=6153194 |date=1980 |last1=Roth |first1=J. |last2=Bendayan |first2=M. |last3=Orci |first3=L. |title=FITC-protein A-gold complex for light and electron microscopic immunocytochemistry |volume=28 |issue=1 |pages=55–7 |journal=Journal of Histochemistry and Cytochemistry |doi=10.1177/28.1.6153194 |doi-access=free}}</ref>

Gold, or alloys of gold and palladium, are applied as conductive coating to biological specimens and other non-conducting materials such as plastics and glass to be viewed in a scanning electron microscope. The coating, which is usually applied by sputtering with an argon plasma, has a triple role in this application. Gold's very high electrical conductivity drains electrical charge to earth, and its very high density provides stopping power for electrons in the electron beam, helping to limit the depth to which the electron beam penetrates the specimen. This improves definition of the position and topography of the specimen surface and increases the spatial resolution of the image. Gold also produces a high output of secondary electrons when irradiated by an electron beam, and these low-energy electrons are the most commonly used signal source used in the scanning electron microscope.<ref>{{Cite book |last1=Bozzola |first1=John J. |last2=Russell |first2=Lonnie Dee |url=https://books.google.com/books?id=RqSMzR-IXk0C&pg=PA65 |page=65 |title=Electron microscopy: principles and techniques for biologists |name-list-style=amp |publisher=Jones & Bartlett Learning |date=1999 |isbn=978-0-7637-0192-5}}</ref>

The isotope gold-198 (half-life 2.7 days) is used in nuclear medicine, in some cancer treatments and for treating other diseases.<ref>{{cite web |url=http://web.missouri.edu/~kattik/katti/katres.html |archive-url=https://web.archive.org/web/20090314121232/http://web.missouri.edu/~kattik/katti/katres.html |archive-date=14 March 2009 |title=Nanoscience and Nanotechnology in Nanomedicine: Hybrid Nanoparticles In Imaging and Therapy of Prostate Cancer |publisher=Radiopharmaceutical Sciences Institute, University of Missouri-Columbia}}</ref><ref>{{cite journal |doi=10.1211/jpp.60.8.0005 |title=Radiotherapy enhancement with gold nanoparticles |date=2008 |last1=Hainfeld |first1=James F. |last2=Dilmanian |first2=F. Avraham |last3=Slatkin |first3=Daniel N. |last4=Smilowitz |first4=Henry M. |s2cid=32861131 |journal=Journal of Pharmacy and Pharmacology |volume=60 |issue=8 |pages=977–85 |pmid=18644191 }}</ref>

=== Cuisine ===
{{CSS image crop
|Image = Dessert (10938449815).jpg
|bSize = 300
|cWidth = 220
|cHeight = 180
|oTop = 20
|oLeft = 52
|Description = Cake with edible gold decoration
}}
* Gold can be used in food and has the E number 175.<ref name="FSA-2007">{{Cite news |url=http://www.food.gov.uk/safereating/chemsafe/additivesbranch/enumberlist |title=Current EU approved additives and their E Numbers |date=27 July 2007 |publisher=Food Standards Agency, UK}}</ref> In 2016, the European Food Safety Authority published an opinion on the re-evaluation of gold as a food additive. Concerns included the possible presence of minute amounts of gold nanoparticles in the food additive, and that gold nanoparticles have been shown to be genotoxic in mammalian cells in vitro.<ref>{{cite journal |title=Scientific Opinion on the re-evaluation of gold (E 175) as a food additive |journal=EFSA Journal |volume=14 |issue=1 |year=2016 |issn=1831-4732 |doi=10.2903/j.efsa.2016.4362 |page=4362|doi-access=free}}</ref>
* Gold leaf, flake or dust is used on and in some gourmet foods, notably sweets and drinks as decorative ingredient.<ref>{{cite web |title=The Food Dictionary: Varak |publisher=Barron's Educational Services, Inc. |date=1995 |url=http://www.epicurious.com/cooking/how_to/food_dictionary/entry?id=5061 |archive-url=https://web.archive.org/web/20060523014547/http://www.epicurious.com/cooking/how_to/food_dictionary/entry?id=5061 |archive-date=23 May 2006 |access-date=27 May 2007}}</ref> Gold flake was used by the nobility in medieval Europe as a decoration in food and drinks,<ref>{{Cite book |url=https://books.google.com/books?id=OMLuBQAAQBAJ&pg=PT94 |title=Commensality: From Everyday Food to Feast |last1=Kerner |first1=Susanne |last2=Chou |first2=Cynthia |last3=Warmind |first3=Morten |page=94 |date=2015 |publisher=Bloomsbury Publishing |isbn=978-0-85785-719-4}}</ref>
* Danziger Goldwasser (German: Gold water of Danzig) or Goldwasser ({{langx|en|Goldwater}}) is a traditional German herbal liqueur<ref>{{Cite book |chapter-url=https://books.google.com/books?id=tsUNAAAAYAAJ&pg=PA101 |title=Deutschland nebst Theilen der angrenzenden Länder |chapter=Danzig |first=Karl |last=Baedeker |date=1865 |publisher=Karl Baedeker |language=de}}</ref> produced in what is today Gdańsk, Poland, and Schwabach, Germany, and contains flakes of gold leaf. There are also some expensive (c. $1000) cocktails which contain flakes of gold leaf. However, since metallic gold is inert to all body chemistry, it has no taste, it provides no nutrition, and it leaves the body unaltered.<ref>{{cite web |url=http://geology.com/minerals/gold/uses-of-gold.shtml |title=The Many Uses of Gold |access-date=6 June 2009 |author=King, Hobart M. |publisher=geology.com}}</ref>
* Vark is a foil composed of a pure metal that is sometimes gold,<ref>[http://www.delafee.com/Edible+Gold+Creations_Information+on+edible+gold/ Gold in Gastronomy] {{Webarchive|url=https://web.archive.org/web/20160304002554/http://www.delafee.com/Edible+Gold+Creations_Information+on+edible+gold/ |date=4 March 2016 }}. deLafee, Switzerland (2008)</ref> and is used for garnishing sweets in South Asian cuisine.

=== Miscellanea ===
[[File:James Webb Space Telescope Mirror33.jpg|thumb|A mirror segment for the James Webb Space Telescope coated in gold to reflect infrared light]]
[[File:Kamakshi Amman Temple with golden roof, Kanchipuram.jpg|thumb|Kamakshi Amman Temple with golden roof, Kanchipuram.]]
* Gold produces a deep, intense red color when used as a coloring agent in cranberry glass.
* In photography, gold toners are used to shift the color of silver bromide black-and-white prints towards brown or blue tones, or to increase their stability. Used on sepia-toned prints, gold toners produce red tones. Kodak published formulas for several types of gold toners, which use gold as the chloride.<ref>[https://web.archive.org/web/20160817134815/http://www.kodak.com/global/en/professional/support/techPubs/g23/g23.pdf Toning black-and-white materials]. Kodak Technical Data/Reference sheet G-23, May 2006.</ref>
* Gold is a good reflector of electromagnetic radiation such as infrared and visible light, as well as radio waves. It is used for the protective coatings on many artificial satellites, in infrared protective faceplates in thermal-protection suits and astronauts' helmets, and in electronic warfare planes such as the EA-6B Prowler.
* Gold is used as the reflective layer on some high-end CDs.
* Automobiles may use gold for heat shielding. McLaren uses gold foil in the engine compartment of its F1 model.<ref>{{cite book |last1=Martin |first1=Keith |url=https://books.google.com/books?id=pUhMRLiHiY8C&pg=PA42 |title=1997 McLaren F1}}</ref>
* Gold can be manufactured so thin that it appears semi-transparent. It is used in some aircraft cockpit windows for de-icing or anti-icing by passing electricity through it. The heat produced by the resistance of the gold is enough to prevent ice from forming.<ref name="GoldBulletin">{{Cite news |url=http://www.goldbulletin.org/assets/file/goldbulletin/downloads/Cooke_2_15.pdf |archive-url=https://web.archive.org/web/20110726122946/http://www.goldbulletin.org/assets/file/goldbulletin/downloads/Cooke_2_15.pdf |archive-date=26 July 2011 |title=The Demand for Gold by Industry |publisher=Gold bulletin |access-date=6 June 2009}}</ref>
* Gold is attacked by and dissolves in alkaline solutions of potassium or sodium cyanide, to form the salt gold cyanide—a technique that has been used in extracting metallic gold from ores in the cyanide process. Gold cyanide is the electrolyte used in commercial electroplating of gold onto base metals and electroforming.
* Gold chloride (chloroauric acid) solutions are used to make colloidal gold by reduction with citrate or ascorbate ions. Gold chloride and gold oxide are used to make cranberry or red-colored glass, which, like colloidal gold suspensions, contains evenly sized spherical gold nanoparticles.<ref>{{cite web |url=http://chemistry.about.com/cs/inorganic/a/aa032503a.htm |title=Colored glass chemistry |access-date=6 June 2009 |archive-date=13 February 2009 |archive-url=https://web.archive.org/web/20090213164051/http://chemistry.about.com/cs/inorganic/a/aa032503a.htm |url-status=dead }}</ref>
* Gold, when dispersed in nanoparticles, can act as a heterogeneous catalyst of chemical reactions.
* In recent years, gold has been used as a symbol of pride by the autism rights movement, as its symbol Au could be seen as similar to the word "autism".<ref>{{cite web |date=2 April 2021 |title=Why 'Going Gold' is important on Autism Acceptance Day. |url=https://edpsy.org.uk/blog/2021/why-going-gold-is-important-on-autism-acceptance-day-2nd-april/ |website=Edpsy}}</ref>

== Toxicity ==
Pure metallic (elemental) gold is non-toxic and non-irritating when ingested<ref>{{cite web |last=Dierks |first=S. |title=Gold MSDS |url=http://www.espi-metals.com/msds's/gold.htm |archive-url=https://web.archive.org/web/20061110104358/http://www.espi-metals.com/msds%27s/gold.htm |url-status=dead |archive-date=10 November 2006 |publisher=Electronic Space Products International |date=May 2005 |access-date=21 December 2021 }}</ref> and is sometimes used as a food decoration in the form of gold leaf.<ref>{{Cite book |url=https://books.google.com/books?id=4zK6CgAAQBAJ&pg=PA5 |title=Gold Nanoparticles for Physics, Chemistry and Biology |last1=Louis |first1=Catherine |last2=Pluchery |first2=Olivier |date=2012 |publisher=World Scientific |isbn=978-1-84816-807-7}}</ref> Metallic gold is also a component of the alcoholic drinks Goldschläger, Gold Strike, and Goldwasser. Metallic gold is approved as a food additive in the EU (E175 in the Codex Alimentarius). Although the gold ion is toxic, the acceptance of metallic gold as a food additive is due to its relative chemical inertness, and resistance to being corroded or transformed into soluble salts (gold compounds) by any known chemical process which would be encountered in the human body.

Soluble compounds (gold salts) such as gold chloride are toxic to the liver and kidneys. Common cyanide salts of gold such as potassium gold cyanide, used in gold electroplating, are toxic by virtue of both their cyanide and gold content. There are rare cases of lethal gold poisoning from potassium gold cyanide.<ref>{{Cite journal |last1=Wright |first1=I. H. |first2=J. C. |last2=Vesey |date=1986 |title=Acute poisoning with gold cyanide |journal=Anaesthesia |volume=41 |issue=79 |pages=936–939 |doi=10.1111/j.1365-2044.1986.tb12920.x |pmid=3022615|s2cid=32434351 |doi-access=free }}</ref><ref>{{Cite journal |last1=Wu |first1=Ming-Ling |first2=Wei-Jen |last2=Tsai |first3=Jiin |last3=Ger |first4=Jou-Fang |last4=Deng |last5=Tsay |first5=Shyh-Haw |display-authors=5 |last6=Yang |first6=Mo-Hsiung |journal=Clinical Toxicology |date=2001 |volume=39 |issue=7 |pages=739–743 |title=Cholestatic Hepatitis Caused by Acute Gold Potassium Cyanide Poisoning |doi=10.1081/CLT-100108516 |pmid=11778673|s2cid=44722156 }}</ref> Gold toxicity can be ameliorated with chelation therapy with an agent such as dimercaprol.

Gold metal was voted Allergen of the Year in 2001 by the American Contact Dermatitis Society; gold contact allergies affect mostly women.<ref name="Tsuruta-2001">{{cite journal |last1=Tsuruta |first1=Kyoko |last2=Matsunaga |first2=Kayoko |last3=Suzuki |first3=Kayoko |last4=Suzuki |first4=Rie |last5=Akita |first5=Hirotaka |last6=Washimi |first6=Yasuko |last7=Tomitaka |first7=Akiko |last8=Ueda |first8=Hiroshi |title=Female predominance of gold allergy |journal=Contact Dermatitis |volume=44 |issue=1 |year=2001 |pages=48–49 |doi=10.1034/j.1600-0536.2001.440107-22.x |pmid=11156030|s2cid=42268840 }}</ref> Despite this, gold is a relatively non-potent contact allergen, in comparison with metals like nickel.<ref>{{Cite news |last=Brunk |first=Doug |url=http://www.highbeam.com/doc/1G1-176478357.html |archive-url=https://web.archive.org/web/20110624033428/http://www.highbeam.com/doc/1G1-176478357.html |url-status=dead |archive-date=24 June 2011 |title=Ubiquitous nickel wins skin contact allergy award for 2008 |date=15 February 2008}}</ref>

A sample of the fungus ''Aspergillus niger'' was found growing from gold mining solution; and was found to contain cyano metal complexes, such as gold, silver, copper, iron and zinc. The fungus also plays a role in the solubilization of heavy metal sulfides.<ref>{{cite book |last=Singh |first=Harbhajan |url=https://books.google.com/books?id=WY3YvfNoouMC&pg=PA533 |title=Mycoremediation: Fungal Bioremediation |page=509 |isbn=978-0-470-05058-3 |date=2006|publisher=John Wiley & Sons }}</ref>

== See also ==
[[File:Pyrit 01.jpg|thumb|right|Iron pyrite or "fool's gold"]]
{{Colbegin|colwidth=20em}}
* Bulk leach extractable gold, for sampling ores
* Chrysiasis (dermatological condition)
* Digital gold currency, form of electronic currency
* GFMS business consultancy
* Gold fingerprinting, use impurities to identify an alloy
* Gold standard in banking
* List of countries by gold production
* Tumbaga, alloy of gold and copper
* Iron pyrite, fool's gold
* Nordic gold, non-gold copper alloy
{{colend}}{{Clear}}

== References ==
{{Reflist|30em}}

== Further reading ==
* Bachmann, H. G. ''The lure of gold : an artistic and cultural history'' (2006) [https://archive.org/details/lureofgold0000unse online]
* Bernstein, Peter L. ''The Power of Gold: The History of an Obsession'' (2000) [https://archive.org/details/powerofgoldhisto00bern online]
* Brands, H.W. ''The Age of Gold: The California Gold Rush and the New American Dream'' (2003) [https://www.amazon.com/Age-Gold-California-American-Recover/dp/0385720882/ excerpt]
* Buranelli, Vincent. ''Gold : an illustrated history'' (1979) [https://archive.org/details/goldillustratedh00bura online]' wide-ranging popular history
* Cassel, Gustav. "The restoration of the gold standard." ''Economica'' 9 (1923): 171–185. [https://www.jstor.org/stable/2548130 online]
* Eichengreen, Barry. ''Golden Fetters: The Gold Standard and the Great Depression, 1919–1939'' (Oxford UP, 1992).
* Ferguson, Niall. ''The Ascent of Money – Financial History of the World'' (2009) [https://archive.org/details/ascentofmoneyf00ferg online]
* Hart, Matthew, [https://books.google.com/books?id=kSI5AAAAQBAJ Gold: The Race for the World's Most Seductive Metal] ''Gold : the race for the world's most seductive metal", New York: Simon & Schuster, 2013. {{ISBN|9781451650020}}''
* {{cite journal | last1 = Johnson | first1 = Harry G | year = 1969 | title = The gold rush of 1968 in retrospect and prospect | journal = American Economic Review | volume = 59 | issue = 2| pages = 344–348 | jstor = 1823687 }}
* Kwarteng, Kwasi. ''War and Gold: A Five-Hundred-Year History of Empires, Adventures, and Debt'' (2014) [https://archive.org/details/wargoldfivehundr0000kwar online]
* Vilar, Pierre. ''A History of Gold and Money, 1450–1920'' (1960). [https://archive.org/details/historyofgoldmon0000vila_c6t2 online]
* Vilches, Elvira. ''New World Gold: Cultural Anxiety and Monetary Disorder in Early Modern Spain'' (2010).

== External links ==
{{Wikiquote|Gold}}
{{Commons}}
{{Wiktionary|gold}}
* {{cite EB1911|wstitle=Gold|volume=11|short=x}}
* [https://web.archive.org/web/20080417110808/http://www.rsc.org/chemistryworld/podcast/element.asp Chemistry in its element podcast] (MP3) from the Royal Society of Chemistry's Chemistry World: [http://www.rsc.org/images/CIIE_Gold_48k_tcm18-118269.mp3 Gold] www.rsc.org
* [http://www.periodicvideos.com/videos/079.htm Gold] at ''The Periodic Table of Videos'' (University of Nottingham)
* [https://web.archive.org/web/20080307000911/http://www.epa.gov/epaoswer/other/mining/techdocs/gold.pdf ''Getting Gold'' 1898 book], www.lateralscience.co.uk
* {{webarchive |url=https://web.archive.org/web/20080307000911/http://www.epa.gov/epaoswer/other/mining/techdocs/gold.pdf |date=7 March 2008 |title=Technical Document on Extraction and Mining of Gold }}, www.epa.gov
* [https://www.rsc.org/periodic-table/element/79/gold Gold element information] – rsc.org

{{Periodic table (navbox)}}
{{Gold compounds}}
{{Jewellery}}
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Category:Chemical elements
Category:Transition metals
Category:Noble metals
Category:Precious metals
Category:Cubic minerals
Category:Minerals in space group 225
Category:Dental materials
Category:Electrical conductors
Category:Native element minerals
Category:E-number additives
Category:Symbols of Alaska
Category:Symbols of California
Category:Chemical elements with face-centered cubic structure
Category:Coinage metals and alloys
Category:Symbols of Victoria

Cybersecurity

2025-05-21T04:28:22Z

Roger.Billings: Created New Article

{{#seo:
|description= Introduction Cybersecurity/Introduction Chapter 1: Fundamentals of Cybersecurity Fundamentals of Cybersecurity serves as the cornerstone for understanding the
}}
{{stub}}

==/Introduction/==
{{/Introduction}}

===/Chapter 1: Fundamentals of Cybersecurity/===
{{/Chapter 1: Fundamentals of Cybersecurity}}
====/Section 1.1: What is Cybersecurity/====
{{/Section 1.1: What is Cybersecurity/}}
====/Section 1.2: Importance of Cybersecurity/====
{{/Section 1.2: Importance of Cybersecurity/}}

===/Chapter 2: Cyber Threats/===
====/Section 2.1: Types of Cyber Threats/====
{{/Section 2.1: Types of Cyber Threats/}}
====/Section 2.2: Common Attack Vectors/====
{{/Section 2.2: Common Attack Vectors/}}

===/Chapter 3: Cybersecurity Layers/===
====/Section 3.1: Network Security/====
{{/Section 3.1: Network Security/}}
====/Section 3.2: Endpoint Security/====
{{/Section 3.2: Endpoint Security/}}
====/Section 3.3: Application Security/====
{{/Section 3.3: Application Security/}}
====/Section 3.4: Physical Security/====
{{/Section 3.4: Physical Security/}}

===/Chapter 4: Security Tools and Technologies/===
====/Section 4.1: Firewalls/====
{{/Section 4.1: Firewalls/}}
====/Section 4.2: Antivirus Software/====
{{/Section 4.2: Antivirus Software/}}
====/Section 4.3: Encryption/====
{{/Section 4.3: Encryption/}}

===/Chapter 5: Security Policies and Procedures/===
====/Section 5.1: Password Policies/====
{{/Section 5.1: Password Policies/}}
====/Section 5.2: Incident Response Plans/====
{{/Section 5.2: Incident Response Plans/}}
====/Section 5.3: Data Backup and Recovery/====
{{/Section 5.3: Data Backup and Recovery/}}

===/Chapter 6: User Education and Awareness/===
====/Section 6.1: Cybersecurity Training/====
{{/Section 6.1: Cybersecurity Training/}}
====/Section 6.2: Recognizing Threats/====
{{/Section 6.2: Recognizing Threats/}}

===/Chapter 7: Legal and Ethical Considerations/===
====/Section 7.1: Data Privacy Laws/====
{{/Section 7.1: Data Privacy Laws/}}
====/Section 7.2: Ethical Hacking and Responsible Disclosure/====
{{/Section 7.2: Ethical Hacking and Responsible Disclosure/}}

===/Chapter 8: Emerging Trends in Cybersecurity/===
====/Section 8.1: AI and Machine Learning in Security/====
{{/Section 8.1: AI and Machine Learning in Security/}}
====/Section 8.2: IoT Security Challenges/====
{{/Section 8.2: IoT Security Challenges/}}
====/Section 8.3: Cloud Security/====
{{/Section 8.3: Cloud Security/}}

===/Chapter 9: Cybersecurity in Different Sectors/===
====/Section 9.1: Business and Corporate Security/====
{{/Section 9.1: Business and Corporate Security/}}
====/Section 9.2: Government and Public Sector Security/====
{{/Section 9.2: Government and Public Sector Security/}}
====/Section 9.3: Home and Personal Security/====
{{/Section 9.3: Home and Personal Security/}}

===/Chapter 10: Resources and Further Reading/===
====/Section 10.1: Cybersecurity Organizations/====
{{/Section 10.1: Cybersecurity Organizations/}}
====/Section 10.2: Books and Online Courses/====
{{/Section 10.2: Books and Online Courses/}}
====/Section 10.3: Useful Websites and Blogs/====
{{/Section 10.3: Useful Websites and Blogs/}}

==/Conclusion/==
{{/Conclusion}}

==/References/==
{{/References}}
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{{Shelves|Information technology|Library and information science}}

Hydrogen Energy

2025-01-15T04:22:11Z

Roger.Billings: Blanked the page

Hydrogen Energy

2025-01-15T04:20:02Z

Roger.Billings: Created page with "{{Short description|Using hydrogen to decarbonize more sectors}} Hydrogen has the most potential to reduce [[greenhouse gas emissions when used in chemical production, refineries, international shipping, and steelmaking<ref>{{Cite web |last=International Renewable Energy Agency |date=2022-03-29 |title=World Energy Transitions Outlook 1-5C Pathway 2022 edition |url=https://www.irena.org/publications/2022/mar..."

{{Short description|Using hydrogen to decarbonize more sectors}}
[[File:IRENA maturity of hydrogen solutions 2022.svg|thumb|Hydrogen has the most potential to reduce [[greenhouse gas emissions]] when used in chemical production, refineries, international shipping, and [[steelmaking]]<ref>{{Cite web |last=International Renewable Energy Agency |date=2022-03-29 |title=World Energy Transitions Outlook 1-5C Pathway 2022 edition |url=https://www.irena.org/publications/2022/mar/world-energy-transitions-outlook-2022 |access-date=2023-10-06 |website=IRENA |page=227 |language=en}}</ref>]]
The '''hydrogen economy''' is an umbrella term for the roles [[hydrogen]] can play alongside [[low-carbon electricity]] to reduce emissions of [[Greenhouse gas|greenhouse gases]]. The aim is to reduce emissions where cheaper and more energy-efficient clean solutions are not available.<ref name=":0" /> In this context, ''hydrogen economy'' encompasses the production of hydrogen and the use of hydrogen in ways that contribute to [[Fossil fuel phase-out|phasing-out fossil fuels]] and limiting [[climate change]].

Hydrogen can be produced by several means. Most hydrogen produced today is ''gray hydrogen'', made from [[natural gas]] through [[Steam reforming|steam methane reforming]] (SMR). This process accounted for 1.8% of global greenhouse gas emissions in 2021.<ref name="auto1">Greenhouse gas emissions totalled 49.3 Gigatonnes CO2e in 2021.{{Cite web |title=Global Greenhouse Gas Emissions: 1990–2020 and Preliminary 2021 Estimates |url=https://rhg.com/research/global-greenhouse-gas-emissions-2021/ |access-date=2023-09-21 |website=Rhodium Group |date=19 December 2022 |language=en-US}}</ref> ''Low-carbon hydrogen'', which is made using SMR with [[carbon capture and storage]] (''[[blue hydrogen]]''), or through electrolysis of water using renewable power (''[[green hydrogen]]''), accounted for less than 1% of production.<ref name=":23">{{Cite web |date=10 July 2023 |title=Hydrogen |url=https://www.iea.org/energy-system/low-emission-fuels/hydrogen |access-date=2023-09-21 |website=IEA |at="Energy" section |language=en-GB}}</ref> Virtually all of the 100 million tonnes<ref>{{Cite web |title=Hydrogen |url=https://www.iea.org/energy-system/low-emission-fuels/hydrogen |access-date=2024-03-24 |website=IEA |language=en-GB}}</ref> of hydrogen produced each year is used in oil refining (43% in 2021) and industry (57%), principally in the manufacture of [[ammonia]] for fertilizers, and [[methanol]].<ref name=":02">{{Cite book |last=IEA |url=https://www.iea.org/reports/global-hydrogen-review-2022 |title=Global Hydrogen Review 2022 |publisher=International Energy Agency |year=2022 |page= |language=en-GB |access-date=2023-08-25}}</ref>{{Rp|pages=18, 22, 29}}

To [[limit global warming]], it is generally envisaged that the future hydrogen economy replaces gray hydrogen with low-carbon hydrogen. As of 2024 it is unclear when enough low-carbon hydrogen could be produced to phase-out all the gray hydrogen.<ref>{{Cite web |title=Hydrogen could be used for nearly everything. It probably shouldn't be. |url=https://www.technologyreview.com/2024/04/25/1091757/hydrogen-uses-ranked/ |access-date=2024-05-13 |website=MIT Technology Review |language=en}}</ref> The future end-uses are likely in heavy industry (e.g. high-temperature processes alongside electricity, feedstock for production of [[Ammonia|green ammonia]] and [[organic chemicals]], as alternative to coal-derived [[Coke (fuel)|coke]] for [[steelmaking]]), long-haul transport (e.g. shipping, and to a lesser extent [[hydrogen-powered aircraft]] and heavy goods vehicles), and long-term energy storage.<ref name=":12">{{Cite book |author=IPCC |author-link=IPCC |url=https://ipcc.ch/report/ar6/wg3/downloads/report/IPCC_AR6_WGIII_FullReport.pdf |title=Climate Change 2022: Mitigation of Climate Change |publisher=Cambridge University Press (In Press) |year=2022 |isbn=9781009157926 |editor1-last=Shukla |editor1-first=P.R. |series=Contribution of Working Group III to the [[IPCC Sixth Assessment Report|Sixth Assessment Report]] of the Intergovernmental Panel on Climate Change |place=Cambridge, UK and New York, NY, US |pages=91–92 |doi=10.1017/9781009157926 |ref={{harvid|IPCC AR6 WG3|2022}} |editor2-last=Skea |editor2-first=J. |editor3-last=Slade |editor3-first=R. |editor4-last=Al Khourdajie |editor4-first=A. |editor5-last=van Diemen |editor5-first=R. |editor6-last=McCollum |editor6-first=D. |editor7-last=Pathak |editor7-first=M. |editor8-last=Some |editor8-first=S. |editor9-last=Vyas |editor9-first=P. |display-editors=4 |editor10-first=R. |editor10-last=Fradera |editor11-first=M. |editor11-last=Belkacemi |editor12-first=A. |editor12-last=Hasija |editor13-first=G. |editor13-last=Lisboa |editor14-first=S. |editor14-last=Luz |editor15-first=J. |editor15-last=Malley}}</ref><ref name="IRENA 2021 95">{{Cite web |last=IRENA |date=2021 |title=World Energy Transitions Outlook: 1.5 °C Pathway |url=https://www.irena.org/publications/2021/Jun/World-Energy-Transitions-Outlook |access-date=2023-09-21 |website=International Renewable Energy Agency |pages=95 |language=en |publication-place=Abu Dhabi}}</ref> Other applications, such as light duty vehicles and heating in buildings, are no longer part of the future hydrogen economy, primarily for economic and environmental reasons.<ref>{{Cite journal |last=Plötz |first=Patrick |date=2022-01-31 |title=Hydrogen technology is unlikely to play a major role in sustainable road transport |url=https://www.nature.com/articles/s41928-021-00706-6 |journal=Nature Electronics |language=en |volume=5 |issue=1 |pages=8–10 |doi=10.1038/s41928-021-00706-6 |s2cid=246465284 |issn=2520-1131}}</ref><ref name=":62">{{Cite journal |last=Rosenow |first=Jan |date=September 2022 |title=Is heating homes with hydrogen all but a pipe dream? An evidence review |journal=Joule |language=en |volume=6 |issue=10 |pages=2225–2228 |doi=10.1016/j.joule.2022.08.015|s2cid=252584593 |doi-access=free |bibcode=2022Joule...6.2225R }}</ref> Hydrogen is challenging to store, to transport in pipelines, and to use. It presents [[Hydrogen safety|safety]] concerns since it is highly explosive, and it is inefficient compared to direct [[Electrification|use of electricity]]. Since relatively small amounts of low-carbon hydrogen are available, climate benefits can be maximized by using it in harder-to-decarbonize applications.<ref name=":62" />

{{As of|2023}} there are no real alternatives to hydrogen for several chemical processes in which it is currently used, such as [[ammonia production]] for [[fertilizer]].<ref>{{Cite web |last=Barnard |first=Michael |date=2023-10-22 |title=What's New On The Rungs Of Liebreich's Hydrogen Ladder? |url=https://cleantechnica.com/2023/10/22/whats-new-on-the-rungs-of-liebreichs-hydrogen-ladder/ |access-date=2024-02-17 |website=CleanTechnica |language=en-US}}</ref> The cost of low- and zero-carbon hydrogen is likely to influence the degree to which it will be used in chemical feedstocks, long haul aviation and shipping, and long-term energy storage. Production costs of low- and zero-carbon hydrogen are evolving. Future costs may be influenced by [[carbon taxes]], the geography and geopolitics of energy, energy prices, technology choices, and their raw material requirements. It is likely that green hydrogen will see the greatest reductions in production cost over time.<ref name="Goldman Sachs Research 4–6">{{Cite web |last=Goldman Sachs Research |title=Carbonomics: The Clean Hydrogen Revolution |url=https://www.goldmansachs.com/intelligence/pages/carbonomics-the-clean-hydrogen-revolution.html |access-date=2023-09-25 |website=Goldman Sachs |pages=4–6 |language=en-US}}</ref> The U.S. Department of Energy's Hydrogen Hotshot Initiative seeks to reduce the cost of green hydrogen drop to $1 a kilogram during the 2030s. <ref name="Hydrogen Hotshot">{{cite web |title=Hydrogen Hotshot Initiative |url=https://www.energy.gov/eere/fuelcells/hydrogen-shot |website=DOE|date=31 August 2021 }}</ref>

== History and objectives ==

=== Origins ===

The concept of a society that uses hydrogen as the primary means of energy storage was theorized by geneticist [[J. B. S. Haldane]] in 1923. Anticipating the exhaustion of Britain's coal reserves for power generation, Haldane proposed a network of wind turbines to produce hydrogen and oxygen for long-term energy storage through [[Electrolysis of water|electrolysis]], to help address renewable power's [[Variable renewable energy|variable output]].<ref>{{Cite web |title=''Daedalus or Science and the Future'', A paper read to the Heretics, Cambridge, on February 4th, 1923 – Transcript 1993 |url=http://bactra.org/Daedalus.html |url-status=live |archive-url=https://web.archive.org/web/20171115013540/http://bactra.org/Daedalus.html |archive-date=2017-11-15 |access-date=2016-01-16}}</ref> The term "hydrogen economy" itself was coined by [[John Bockris]] during a talk he gave in 1970 at [[General Motors]] (GM) Technical Center.<ref name="timeline">{{cite web|url=http://www.hydrogenassociation.org/general/factSheet_history.pdf|title=The History of Hydrogen|author1=National Hydrogen Association|author2=United States Department of Energy|work=hydrogenassociation.org|publisher=National Hydrogen Association|page=1|access-date=17 December 2010|url-status=dead|archive-url=https://web.archive.org/web/20100714141058/http://www.hydrogenassociation.org/general/factSheet_history.pdf|archive-date=14 July 2010}}</ref> Bockris viewed it as an economy in which hydrogen, underpinned by [[Nuclear power|nuclear]] and [[Solar power|solar]] power, would help address growing concern about fossil fuel depletion and environmental pollution, by serving as [[energy carrier]] for end-uses in which [[electrification]] was not suitable.<ref name=":0">{{Cite journal |last1=Yap |first1=Jiazhen |last2=McLellan |first2=Benjamin |date=6 January 2023 |title=A Historical Analysis of Hydrogen Economy Research, Development, and Expectations, 1972 to 2020 |journal=Environments |language=en |volume=10 |issue=1 |pages=11 |doi=10.3390/environments10010011 |issn=2076-3298 |doi-access=free |hdl=2433/284015 |hdl-access=free }}</ref><ref>{{Cite journal |last=Bockris |first=J. O'M. |date=1972-06-23 |title=A Hydrogen Economy |url=https://www.science.org/doi/10.1126/science.176.4041.1323 |journal=Science |language=en |volume=176 |issue=4041 |pages=1323 |doi=10.1126/science.176.4041.1323 |pmid=17820918 |bibcode=1972Sci...176.1323O |issn=0036-8075}}</ref>

A hydrogen economy was proposed by the [[University of Michigan]] to solve some of the negative effects of using [[hydrocarbon]] fuels where the carbon is released to the atmosphere (as carbon dioxide, carbon monoxide, unburnt hydrocarbons, etc.). Modern interest in the hydrogen economy can generally be traced to a 1970 technical report by [[Lawrence W. Jones]] of the University of Michigan,<ref>{{cite conference|last1=Jones|first1=Lawrence W|date=13 March 1970|title=Toward a liquid hydrogen fuel economy|conference=University of Michigan Environmental Action for Survival Teach In|location=Ann Arbor, Michigan|publisher=[[University of Michigan]]|hdl=2027.42/5800}}</ref> in which he echoed Bockris' dual rationale of addressing energy security and environmental challenges. Unlike Haldane and Bockris, Jones only focused on nuclear power as the energy source for electrolysis, and principally on the use of hydrogen in transport, where he regarded aviation and heavy goods transport as the top priorities.<ref>{{Cite book |last=Jones |first=Lawrence W. |url=https://deepblue.lib.umich.edu/bitstream/handle/2027.42/5800/bac5758.0001.001.pdf |title=Toward a Liquid Hydrogen Fuel Economy |date=March 13, 1970 |pages=2–3}}</ref>

=== Later evolution ===
[[File:IRENA hydrogen leadership opportunities.png|thumb|Technology leadership opportunities in green hydrogen value chains according to the [[International Renewable Energy Agency]] in 2022<ref>IRENA (2022), [https://www.irena.org/Publications/2022/Jan/Geopolitics-of-the-Energy-Transformation-Hydrogen Geopolitics of the Energy Transformation: The Hydrogen Factor], International Renewable Energy Agency, Abu Dhabi. {{ISBN|978-92-9260-370-0}}.</ref>{{rp|55}}]]
A spike in attention for the ''hydrogen economy'' concept during the 2000s was repeatedly described as hype by some [[The Hype about Hydrogen|critics]] and proponents of alternative technologies,<ref>{{cite journal |last1=Bakker |first1=Sjoerd |title=The car industry and the blow-out of the hydrogen hype |journal=Energy Policy |volume=38 |issue=11 |pages=6540–6544 |doi=10.1016/j.enpol.2010.07.019 |year=2010 |bibcode=2010EnPol..38.6540B |url=http://www.geo.uu.nl/isu/pdf/isu0914.pdf |access-date=2019-12-11 |archive-date=2018-11-03 |archive-url=https://web.archive.org/web/20181103054549/http://www.geo.uu.nl/isu/pdf/isu0914.pdf |url-status=live }}</ref><ref>{{cite journal|last1=Harrison|first1=James|title=Reactions: Hydrogen hype|journal=Chemical Engineer|volume=58|pages=774–775|url=https://www.scopus.com/inward/record.url?eid=2-s2.0-31644446919&partnerID=40&md5=774f9bad3596ab20fa4e09dd311650f9|access-date=2017-08-31|archive-date=2021-02-08|archive-url=https://web.archive.org/web/20210208150534/https://www.scopus.com/record/display.uri?eid=2-s2.0-31644446919&origin=inward&txGid=991e7333984829c38848e466307c1bde|url-status=live}}</ref><ref>{{cite journal|last1=Rizzi, Francesco Annunziata, Eleonora Liberati, Guglielmo Frey, Marco|title=Technological trajectories in the automotive industry: are hydrogen technologies still a possibility?|journal=Journal of Cleaner Production|date=2014 |volume=66|pages=328–336 |doi=10.1016/j.jclepro.2013.11.069|bibcode=2014JCPro..66..328R }}</ref> and investors lost money in the [[Economic bubble|bubble]].<ref name=":1">{{Cite news |title=Can a viable industry emerge from the hydrogen shakeout? |newspaper=The Economist |url=https://www.economist.com/business/2023/07/03/can-a-viable-industry-emerge-from-the-hydrogen-shakeout |access-date=2023-09-26 |issn=0013-0613}}</ref> Interest in the energy carrier resurged in the 2010s, notably with the forming of the [[World Hydrogen Council]] in 2017. Several manufacturers released hydrogen fuel cell cars commercially, with manufacturers such as Toyota, Hyundai, and industry groups in China having planned to increase numbers of the cars into the hundreds of thousands over the next decade.<ref>{{cite news|last1=Murai|first1=Shusuke|title=Japan's top auto and energy firms tie up to promote development of hydrogen stations|url=https://www.japantimes.co.jp/news/2018/03/05/business/japans-top-auto-energy-firms-tie-promote-development-hydrogen-stations/|newspaper=The Japan Times Online|publisher=Japan Times|access-date=16 April 2018|date=2018-03-05|archive-date=2018-04-17|archive-url=https://web.archive.org/web/20180417194850/https://www.japantimes.co.jp/news/2018/03/05/business/japans-top-auto-energy-firms-tie-promote-development-hydrogen-stations/|url-status=live}}</ref><ref>{{cite web|last1=Mishra|first1=Ankit|title=Prospects of fuel-cell electric vehicles boosted with Chinese backing|url=http://energypost.eu/fuel-cell-vehicles-help-drive-china-to-a-low-carbon-future/|publisher=Energy Post|access-date=16 April 2018|date=2018-03-29|archive-date=2018-04-17|archive-url=https://web.archive.org/web/20180417192045/http://energypost.eu/fuel-cell-vehicles-help-drive-china-to-a-low-carbon-future/|url-status=live}}</ref>

The global scope for hydrogen's role in cars is shrinking relative to earlier expectations.<ref name="role2">{{Cite journal |last=Plötz |first=Patrick |date=January 2022 |title=Hydrogen technology is unlikely to play a major role in sustainable road transport |url=https://www.nature.com/articles/s41928-021-00706-6 |journal=Nature Electronics |volume=5 |issue=1 |pages=8–10 |doi=10.1038/s41928-021-00706-6 |s2cid=246465284 |issn=2520-1131}}</ref><ref name="Collins l_collins2">{{Cite news |last=Collins (l_collins) |first=Leigh |date=2022-02-02 |title='Hydrogen unlikely to play major role in road transport, even for heavy trucks': Fraunhofer |url=https://www.rechargenews.com/energy-transition/-hydrogen-unlikely-to-play-major-role-in-road-transport-even-for-heavy-trucks-fraunhofer/2-1-1162055 |access-date=2023-09-08 |newspaper=Recharge | Latest Renewable Energy News}}</ref> By the end of 2022, 70,200 [[hydrogen vehicle]]s had been sold worldwide,<ref name="auto2">{{Cite book |last1=Chu |first1=Yidan |url=https://theicct.org/wp-content/uploads/2023/06/Global-EV-sales-2022_FINAL.pdf |title=Annual update on the global transition to electric vehicles: 2022 |last2=Cui |first2=Hongyang |publisher=International Council on Clean Transportation |pages=2–3 |access-date=2023-08-25}}</ref> compared with 26 million [[plug-in electric vehicle]]s.<ref name="Outlook2023">{{Cite book |url=https://www.iea.org/reports/global-ev-outlook-2023 |title=Global EV Outlook 2023 |date=26 April 2023 |publisher=IEA |pages=14–24 |access-date=2023-08-25}}</ref>

Early 2020s takes on the hydrogen economy share earlier perspectives' emphasis on the complementarity of electricity and hydrogen, and the use of electrolysis as the mainstay of hydrogen production.<ref name=":12"/> They focus on the need to limit [[Climate change|global warming]] to 1.5 °C and prioritize the production, transportation and use of [[green hydrogen]] for heavy industry (e.g. high-temperature processes alongside electricity,<ref name="Kjellberg-Motton">{{Cite web |last=Kjellberg-Motton |first=Brendan |date=2022-02-07 |title=Steel decarbonisation gathers speed {{!}} Argus Media |url=https://www.argusmedia.com/en//news/2299399-steel-decarbonisation-gathers-speed |access-date=2023-09-07 |website=www.argusmedia.com |language=en}}</ref> feedstock for production of [[green ammonia]] and organic chemicals,<ref name=":12"/> as alternative to coal-derived coke for [[steelmaking]]),<ref name="auto">{{Cite web |last1=Blank |first1=Thomas |last2=Molly |first2=Patrick |date=January 2020 |title=Hydrogen's Decarbonization Impact for Industry |url=https://rmi.org/wp-content/uploads/2020/01/hydrogen_insight_brief.pdf |url-status=live |archive-url=https://web.archive.org/web/20200922115313/https://rmi.org/wp-content/uploads/2020/01/hydrogen_insight_brief.pdf |archive-date=22 September 2020 |access-date= |publisher=[[Rocky Mountain Institute]] |pages=2, 7, 8}}</ref> long-haul transport (e.g. shipping, aviation and to a lesser extent heavy goods vehicles), and long-term energy storage.<ref name=":12" /><ref name="IRENA 2021 95"/>

==Current hydrogen market==
[[Hydrogen production]] globally was valued at over US$155 billion in 2022 and is expected to grow over 9% annually through 2030.<ref>{{Cite web |title=Hydrogen Generation Market Size, Share & Trends Analysis Report, 2023 – 2030 |url=https://www.grandviewresearch.com/industry-analysis/hydrogen-generation-market |access-date=2023-08-30 |website=www.grandviewresearch.com |language=en}}</ref>

In 2021, 94 million tonnes (Mt) of molecular hydrogen ({{chem2|H2}}) was produced.<ref>{{Cite web |title=Executive summary – Global Hydrogen Review 2022 – Analysis |url=https://www.iea.org/reports/global-hydrogen-review-2022/executive-summary |access-date=2023-09-21 |website=IEA |language=en-GB}}</ref> Of this total, approximately one sixth was as a by-product of [[petrochemical industry]] processes.<ref name=":23"/> Most hydrogen comes from dedicated production facilities, over 99% of which is from fossil fuels, mainly via steam reforming of natural gas (70%) and coal gasification (30%, almost all of which in China).<ref name=":23"/> Less than 1% of dedicated hydrogen production is low carbon: steam fossil fuel reforming with [[carbon capture and storage]], [[green hydrogen]] produced using electrolysis, and hydrogen produced from [[Biomass (energy)|biomass]].<ref name=":23"/> CO2 emissions from 2021 production, at 915 MtCO2,<ref>{{Cite web |title=Hydrogen |url=https://www.iea.org/energy-system/low-emission-fuels/hydrogen |access-date=2023-09-21 |website=IEA |language=en-GB}}</ref> amounted to 2.5% of energy-related CO2 emissions<ref>Energy-related emissions totalled 36.3 Gigatonnes CO2 in 2021.{{Cite web |title=Global CO2 emissions rebounded to their highest level in history in 2021 – News |url=https://www.iea.org/news/global-co2-emissions-rebounded-to-their-highest-level-in-history-in-2021 |access-date=2023-09-21 |website=IEA |date=8 March 2022 |language=en-GB}}</ref> and 1.8% of global greenhouse gas emissions.<ref name="auto1"/>

Virtually all hydrogen produced for the current market is used in [[oil refining]] (40 Mt{{chem2|H2}} in 2021) and industry (54 MtH2).<ref name=":02"/>{{Rp|pages=18, 22}} In oil refining, hydrogen is used, in a process known as [[hydrocracking]], to convert heavy petroleum sources into lighter fractions suitable for use as fuels. Industrial uses mainly comprise [[ammonia]] production to make fertilizers (34 Mt{{chem2|H2}} in 2021), [[methanol]] production (15 Mt{{chem2|H2}}) and the manufacture of [[direct reduced iron]] (5 Mt{{chem2|H2}}).<ref name=":02" />{{Rp|pages=|page=29}}

== Production ==
{{Excerpt|Hydrogen production|paragraphs=1-3}}

===Green methanol===
{{See also|Methanol economy}}
Green [[methanol fuel|methanol]] is a [[liquid fuel]] that is produced from combining [[carbon dioxide]] and [[hydrogen]] ({{chem2|CO2 + 3 H2 → CH3OH + H2O}}) under pressure and heat with [[Catalyst support|catalysts]]. It is a way to reuse [[carbon capture and recycling|carbon capture for recycling]]. Methanol can store hydrogen economically at [[Standard temperature and pressure|standard outdoor temperatures and pressures]], compared to [[liquid hydrogen]] and [[ammonia]] that need to use a lot of energy to stay cold in their [[liquid state]].<ref>{{Cite journal |last1=Song |first1=Qianqian |last2=Tinoco |first2=Rodrigo Rivera |last3=Yang |first3=Haiping |last4=Yang |first4=Qing |last5=Jiang |first5=Hao |last6=Chen |first6=Yingquan |last7=Chen |first7=Hanping |date=2022-09-01 |title=A comparative study on energy efficiency of the maritime supply chains for liquefied hydrogen, ammonia, methanol and natural gas |journal=Carbon Capture Science & Technology |volume=4 |pages=100056 |doi=10.1016/j.ccst.2022.100056 |issn=2772-6568|doi-access=free }}</ref> In 2023 the [[Laura Maersk (2023)|Laura Maersk]] was the first container ship to run on methanol fuel.<ref>{{Cite web |date=2023-09-14 |title=World's 'first green container ship' christened in Denmark |url=https://www.euronews.com/green/2023/09/14/what-is-green-methanol-denmark-launches-the-worlds-first-green-container-ship |access-date=2024-08-14 |website=euronews |language=en}}</ref> [[Ethanol fuel|Ethanol plants]] in the midwest are a good place for pure carbon capture to combine with hydrogen to make green methanol, with abundant [[Wind power in the United States|wind]] and [[Nuclear power in the United States|nuclear energy]] in [[wind power in Iowa|Iowa]], [[Wind power in Minnesota|Minnesota]], and [[List of power stations in Illinois|Illinois]].<ref>{{Cite web |last=Strong |first=Jared |date=2024-02-17 |title=Green methanol: A carbon dioxide pipeline alternative? • Nebraska Examiner |url=https://nebraskaexaminer.com/2024/02/17/green-methanol-a-carbon-dioxide-pipeline-alternative/ |access-date=2024-08-14 |website=Nebraska Examiner |language=en-US}}</ref><ref>{{Cite journal |last1=Cordero-Lanzac |first1=Tomas |last2=Ramirez |first2=Adrian |last3=Navajas |first3=Alberto |last4=Gevers |first4=Lieven |last5=Brunialti |first5=Sirio |last6=Gandía |first6=Luis M. |last7=Aguayo |first7=Andrés T. |last8=Mani Sarathy |first8=S. |last9=Gascon |first9=Jorge |date=2022-05-01 |title=A techno-economic and life cycle assessment for the production of green methanol from CO2: catalyst and process bottlenecks |url=https://www.sciencedirect.com/science/article/pii/S2095495621005738 |journal=Journal of Energy Chemistry |volume=68 |pages=255–266 |doi=10.1016/j.jechem.2021.09.045 |issn=2095-4956|hdl=10754/673022 |hdl-access=free }}</ref> Mixing methanol with [[ethanol]] could make methanol a safer fuel to use because methanol doesn't have a visible flame in the daylight and doesn't emit smoke, and ethanol has a visible light yellow flame.<ref>{{cite journal | url=https://pubs.acs.org/doi/10.1021/acsomega.2c00991 | doi=10.1021/acsomega.2c00991 | title=Effects of Ethanol and Methanol on the Combustion Characteristics of Gasoline with the Revised Variation Disturbance Method | date=2022 | last1=Li | first1=Shu-hao | last2=Wen | first2=Zhenhua | last3=Hou | first3=Junxing | last4=Xi | first4=Shuanghui | last5=Fang | first5=Pengya | last6=Guo | first6=Xiao | last7=Li | first7=Yong | last8=Wang | first8=Zhenghe | last9=Li | first9=Shangjun | journal=ACS Omega | volume=7 | issue=21 | pages=17797–17810 | pmc=9161270 }}</ref><ref>{{cite web | url=https://www.youtube.com/watch?v=lmEsU-QYxNk | title=The Horror of Methanol Fires | Last Moments | website=[[YouTube]] | date=17 March 2023 }}</ref><ref>{{cite web | url=https://www.freepatentsonline.com/5858031.html | title=Isopropanol blended with aqueous ethanol for flame coloration without use of salts or hazardous solvents }}</ref> [[Green hydrogen]] production of 70% efficiency and a 70% efficiency of methanol production from that would be a 49% [[energy conversion efficiency]].<ref>{{Cite web |title=Green Methanol Production-A Techno-Economic Analysis |url=https://www.linkedin.com/pulse/green-methanol-production-a-techno-economic-analysis-clrkc |access-date=2024-08-14 |website=www.linkedin.com |language=en}}</ref>

==Uses==
[[File:The_Hydrogen_Ladder,_Version_5.0.jpg|thumb|Some projected uses in the medium term, but analysts disagree<ref>{{Cite web |last=Barnard |first=Michael |date=2023-10-22 |title=What's New On The Rungs Of Liebreich's Hydrogen Ladder? |url=https://cleantechnica.com/2023/10/22/whats-new-on-the-rungs-of-liebreichs-hydrogen-ladder/ |access-date=2024-03-10 |website=CleanTechnica |language=en-US}}</ref>]]
[[Image:Photo praxair plant.hydrogen.infrastructure.jpg|thumb|200px|right|Hydrogen fuel requires the development of a specific infrastructure for processing, transport and storage.]]
Hydrogen can be deployed as a fuel in two distinct ways: in [[fuel cells]] which produce electricity, and via combustion to generate heat.<ref name=":04">{{Cite journal |last=Lewis |first=Alastair C. |date=10 June 2021 |title=Optimising air quality co-benefits in a hydrogen economy: a case for hydrogen-specific standards for NO x emissions |journal=Environmental Science: Atmospheres |language=en |volume=1 |issue=5 |pages=201–207 |doi=10.1039/D1EA00037C|s2cid=236732702 |doi-access=free }}{{Creative Commons text attribution notice|cc=by3|url=|authors=|vrt=|from this source=yes}}</ref> When hydrogen is consumed in fuel cells, the only emission at the point of use is water vapor.<ref name=":04" /> Combustion of hydrogen can lead to the thermal formation of harmful [[NOx|nitrogen oxides]] emissions.<ref name=":04" />

=== Industry ===
In the context of [[limiting global warming]], low-carbon hydrogen (particularly [[green hydrogen]]) is likely to play an important role in decarbonizing industry.<ref name=":122">{{Cite book |author=IPCC |url=https://ipcc.ch/report/ar6/wg3/downloads/report/IPCC_AR6_WGIII_FullReport.pdf |title=Climate Change 2022: Mitigation of Climate Change |publisher=Cambridge University Press (In Press) |year=2022 |editor1-last=Shukla |editor1-first=P.R. |series=Contribution of Working Group III to the [[IPCC Sixth Assessment Report|Sixth Assessment Report]] of the Intergovernmental Panel on Climate Change |place=Cambridge, UK and New York, NY, US |pages=1184 |doi=10.1017/9781009157926 |isbn=9781009157926 |ref={{harvid|IPCC AR6 WG3|2022}} |author-link=IPCC |editor2-last=Skea |editor2-first=J. |editor3-last=Slade |editor3-first=R. |editor4-last=Al Khourdajie |editor4-first=A. |editor5-last=van Diemen |editor5-first=R. |editor6-last=McCollum |editor6-first=D. |editor7-last=Pathak |editor7-first=M. |editor8-last=Some |editor8-first=S. |editor9-last=Vyas |editor9-first=P. |display-editors=4 |editor10-first=R. |editor10-last=Fradera |editor11-first=M. |editor11-last=Belkacemi |editor12-first=A. |editor12-last=Hasija |editor13-first=G. |editor13-last=Lisboa |editor14-first=S. |editor14-last=Luz |editor15-first=J. |editor15-last=Malley}}</ref> Hydrogen fuel can produce the intense heat required for industrial production of steel, cement, glass, and chemicals, thus contributing to the decarbonization of industry alongside other technologies, such as [[electric arc furnace]]s for steelmaking.<ref name="Kjellberg-Motton"/> However, it is likely to play a larger role in providing industrial feedstock for cleaner production of ammonia and organic chemicals.<ref name=":122" /> For example, in [[steelmaking]], hydrogen could function as a clean energy carrier and also as a low-carbon catalyst replacing coal-derived [[Coke (fuel)|coke]].<ref name="auto"/>

The imperative to use low-carbon hydrogen to reduce greenhouse gas emissions has the potential to reshape the geography of industrial activities, as locations with appropriate hydrogen production potential in different regions will interact in new ways with logistics infrastructure, raw material availability, human and technological capital.<ref name=":122" />

=== Transport===
{{Main|Hydrogen vehicle}}

Much of the interest in the hydrogen economy concept is focused on [[hydrogen vehicle]]s, particularly [[Hydrogen plane|planes]].<ref>{{Cite news |title=Is the time now ripe for planes to run on hydrogen? |url=https://www.economist.com/science-and-technology/2020/12/08/is-the-time-now-ripe-for-planes-to-run-on-hydrogen |access-date=2024-02-17 |newspaper=The Economist |issn=0013-0613}}</ref><ref>{{Cite journal |last1=Yusaf |first1=Talal |last2=Faisal Mahamude |first2=Abu Shadate |last3=Kadirgama |first3=Kumaran |last4=Ramasamy |first4=Devarajan |last5=Farhana |first5=Kaniz |last6=A. Dhahad |first6=Hayder |last7=Abu Talib |first7=ABD Rahim |date=2024-01-02 |title=Sustainable hydrogen energy in aviation – A narrative review |journal=International Journal of Hydrogen Energy |volume=52 |pages=1026–1045 |doi=10.1016/j.ijhydene.2023.02.086 |issn=0360-3199|doi-access=free |bibcode=2024IJHE...52.1026Y }}</ref> Hydrogen vehicles produce significantly less local air pollution than conventional vehicles.<ref>{{cite web |date=2018-02-16 |title=This company may have solved one of the hardest problems in clean energy |url=https://www.vox.com/energy-and-environment/2018/2/16/16926950/hydrogen-fuel-technology-economy-hytech-storage |url-status=live |archive-url=https://web.archive.org/web/20191112094756/https://www.vox.com/energy-and-environment/2018/2/16/16926950/hydrogen-fuel-technology-economy-hytech-storage |archive-date=2019-11-12 |access-date=9 February 2019 |publisher=Vox}}</ref> By 2050, the energy requirement for transportation might be between 20% and 30% fulfilled by hydrogen and [[synthetic fuel]]s.<ref>{{Cite web |last=IRENA |title=The Hydrogen Factor |url=https://irena.org/DigitalArticles/2022/Jan/Hydrogen_Factor |access-date=2022-10-19 |website=irena.org |language=en |archive-date=2022-10-19 |archive-url=https://web.archive.org/web/20221019161220/https://irena.org/DigitalArticles/2022/Jan/Hydrogen_Factor |url-status=dead }}</ref><ref>{{Cite web |title=Sustainable fuels and their role in decarbonizing energy {{!}} McKinsey |url=https://www.mckinsey.com/industries/oil-and-gas/our-insights/charting-the-global-energy-landscape-to-2050-sustainable-fuels |access-date=2022-10-19 |website=www.mckinsey.com}}</ref><ref>{{Cite journal |last1=Spiryagin |first1=Maksym |last2=Dixon |first2=Roger |last3=Oldknow |first3=Kevin |last4=Cole |first4=Colin |date=2021-09-01 |title=Preface to special issue on hybrid and hydrogen technologies for railway operations |journal=Railway Engineering Science |language=en |volume=29 |issue=3 |pages=211 |doi=10.1007/s40534-021-00254-x |issn=2662-4753 |s2cid=240522190 |doi-access=free|bibcode=2021RailE..29..211S }}</ref>

Hydrogen used to decarbonize transportation is likely to find its largest applications in [[Hydrogen-powered ship|shipping]], aviation and to a lesser extent heavy goods vehicles, through the use of hydrogen-derived synthetic fuels such as [[Green ammonia|ammonia]] and [[Green methanol|methanol]], and fuel cell technology.<ref name=":12"/> Hydrogen has been used in [[fuel cell bus]]es for many years. It is also used as a fuel for [[spacecraft propulsion]].

In the [[International Energy Agency]]'s 2022 Net Zero Emissions Scenario (NZE), hydrogen is forecast to account for 2% of rail energy demand in 2050, while 90% of rail travel is expected to be electrified by then (up from 45% today). Hydrogen's role in rail would likely be focused on lines that prove difficult or costly to electrify.<ref>{{Cite book |url=https://www.iea.org/reports/world-energy-outlook-2022 |title=World energy outlook 2022 |date=27 October 2022 |publisher=International Energy Agency |pages=150}}{{Creative Commons text attribution notice|cc=by4|from this source=yes}}</ref> The NZE foresees hydrogen meeting approximately 30% of [[heavy truck]] energy demand in 2050, mainly for long-distance heavy freight (with battery electric power accounting for around 60%).<ref>{{Cite book |last1=Cozzi |first1=Laura |url=https://iea.blob.core.windows.net/assets/830fe099-5530-48f2-a7c1-11f35d510983/WorldEnergyOutlook2022.pdf |title=World Energy Outlook 2022 |last2=Gould |first2=Tim |publisher=International Energy Agency |pages=148}}{{Creative Commons text attribution notice|cc=by4|from this source=yes}}</ref>

Although hydrogen can be used in adapted [[Hydrogen internal combustion engine vehicle|internal combustion engines]], fuel cells, being [[electrochemical]], have an efficiency advantage over heat engines. Fuel cells are more expensive to produce than common internal combustion engines but also require higher purity hydrogen fuel than internal combustion engines.<ref>{{Cite journal |last=Stępień |first=Zbigniew |date=January 2021 |title=A Comprehensive Overview of Hydrogen-Fueled Internal Combustion Engines: Achievements and Future Challenges |journal=Energies |language=en |volume=14 |issue=20 |pages=6504 |doi=10.3390/en14206504 |issn=1996-1073 |doi-access=free }}</ref>

In the light road vehicle segment including passenger cars, by the end of 2022, 70,200 fuel cell electric vehicles had been sold worldwide,<ref name="auto2" /> compared with 26 million plug-in electric vehicles.<ref name="Outlook2023" /> With the rapid rise of [[electric vehicle]]s and associated battery technology and infrastructure, hydrogen's role in cars is minuscule.<ref name="role2" /><ref name="Collins l_collins2" />

=== Energy system balancing and storage ===
[[Green hydrogen]], from [[electrolysis of water]], has the potential to address the [[Variable renewable energy|variability of renewable energy]] output. Producing green hydrogen can both reduce the need for renewable power [[Curtailment (electricity)|curtailment]] during periods of high renewables output and be [[Energy storage|stored]] long-term to provide for power generation during periods of low output.<ref name="Schrotenboer">{{Cite journal |last1=Schrotenboer |first1=Albert H. |last2=Veenstra |first2=Arjen A.T. |last3=uit het Broek |first3=Michiel A.J. |last4=Ursavas |first4=Evrim |date=October 2022 |title=A Green Hydrogen Energy System: Optimal control strategies for integrated hydrogen storage and power generation with wind energy |url=https://pure.rug.nl/ws/portalfiles/portal/230184233/1_s2.0_S1364032122006323_main.pdf |journal=Renewable and Sustainable Energy Reviews |language=en |volume=168 |pages=112744 |doi=10.1016/j.rser.2022.112744 |arxiv=2108.00530 |bibcode=2022RSERv.16812744S |s2cid=250941369}}</ref><ref name="Lipták">{{Cite news |last=Lipták |first=Béla |date=January 24, 2022 |title=Hydrogen is key to sustainable green energy |work=Control |url=https://www.controlglobal.com/home/article/11288951/hydrogen-is-key-to-sustainable-green-energy |access-date=February 12, 2023}}</ref>

===Ammonia ===

{{Main|ammonia|ammonia production}}

{{see also|alkaline fuel cell}}
An alternative to gaseous hydrogen as an energy carrier is to bond it with [[nitrogen]] from the air to produce ammonia, which can be easily liquefied, transported, and used (directly or indirectly) as a clean and [[Ammonia as a fuel|renewable fuel]].<ref>{{cite web |last=Agosta |first=Vito |date=July 10, 2003 |title=The Ammonia Economy |url=http://www.memagazine.org/contents/current/webonly/webex710.html |url-status=dead |archive-url=https://web.archive.org/web/20080513030624/http://www.memagazine.org/contents/current/webonly/webex710.html |archive-date=May 13, 2008 |access-date=2008-05-09}}</ref><ref>{{cite web |title=Renewable Energy |url=http://www.energy.iastate.edu/Renewable/ammonia/index.htm |url-status=dead |archive-url=https://web.archive.org/web/20080513191842/http://www.energy.iastate.edu/renewable/ammonia/index.htm |archive-date=2008-05-13 |access-date=2008-05-09 |publisher=Iowa Energy Center}}</ref> Among disadvantages of ammonia as an energy carrier are its high toxicity, energy efficiency of {{chem2|NH3}} production from {{chem2|N2}} and {{chem2|H2}}, and poisoning of [[Fuel cell|PEM Fuel Cells]] by traces of non-decomposed {{chem2|NH3}} after {{chem2|NH3}} to {{chem2|N2}} conversion.

=== Buildings ===
Numerous industry groups (gas networks, [[gas boiler]] manufacturers) across the natural gas supply chain are promoting hydrogen combustion boilers for space and water heating, and hydrogen appliances for cooking, to reduce energy-related CO2 emissions from residential and commercial buildings.<ref name=":5">{{Cite web |last=Collins |first=Leigh |date=2021-12-10 |title=Even the European gas lobby can't make a case for hydrogen boilers — so why does it say gases are needed to decarbonise heating? |url=https://www.rechargenews.com/energy-transition/even-the-european-gas-lobby-can-t-make-a-case-for-hydrogen-boilers-so-why-does-it-say-gases-are-needed-to-decarbonise-heating-/2-1-1120847 |access-date=2023-09-25 |website=Recharge {{!}} Latest renewable energy news |language=en}}</ref><ref name=":7">{{Cite web |last=Roth |first=Sammy |date=2023-02-09 |title=California declared war on natural gas. Now the fight is going national |url=https://www.latimes.com/environment/newsletter/2023-02-09/california-declared-war-on-natural-gas-now-the-fight-is-going-national-boiling-point |access-date=2023-09-25 |website=Los Angeles Times |language=en-US}}</ref><ref name=":62" /> The proposition is that current end-users of piped natural gas can await the conversion of and supply of hydrogen to existing [[Natural gas#Domestic use|natural gas grids]], and then swap heating and cooking appliances, and that there is no need for consumers to do anything now.<ref name=":5" /><ref name=":7" /><ref name=":62" />

A review of 32 studies on the question of hydrogen for heating buildings, independent of commercial interests, found that the economics and climate benefits of hydrogen for heating and cooking generally compare very poorly with the deployment of [[district heating]] networks, electrification of heating (principally through [[heat pump]]s) and cooking, the use of [[Solar thermal energy|solar thermal]], [[waste heat]] and the installation of [[Energy efficient building|energy efficiency]] measures to reduce energy demand for heat.<ref name=":62" /> Due to inefficiencies in hydrogen production, using blue hydrogen to replace natural gas for heating could require three times as much [[methane]], while using green hydrogen would need two to three times as much electricity as heat pumps.<ref name=":62" /> Hybrid heat pumps, which combine the use of an electric heat pump with a hydrogen boiler, may play a role in residential heating in areas where upgrading networks to meet peak electrical demand would otherwise be costly.<ref name=":62" />

The widespread use of hydrogen for heating buildings would entail higher energy system costs, higher heating costs and higher environmental impacts than the alternatives, although a niche role may be appropriate in specific contexts and geographies.<ref name=":62" /> If deployed, using hydrogen in buildings would drive up the cost of hydrogen for harder-to-decarbonize applications in industry and transport.<ref name=":62" />

===Bio-SNG===
{{As of|2019}} although technically possible [[Syngas#Carbon dioxide and hydrogen|production of syngas from hydrogen and carbon-dioxide]] from [[bio-energy with carbon capture and storage]] (BECCS) via the [[Sabatier reaction]] is limited by the amount of sustainable bioenergy available:<ref>{{Harvnb|UKCCC H2|2018|p=79}}: The potential for bio-gasification with CCS to be deployed at scale is limited by the amount of sustainable bioenergy available. .... "</ref> therefore any [[bio-SNG]] made may be reserved for production of [[aviation biofuel]].<ref>{{Harvnb|UKCCC H2|2018|p=33}}: production of biofuels, even with CCS, is only one of the best uses of the finite sustainable bio-resource if the fossil fuels it displaces cannot otherwise feasibly be displaced (e.g. use of biomass to produce aviation biofuels with CCS)."</ref>

== Safety ==
{{Main|Hydrogen safety}}
[[File:Hydrogen Flame Broom Test NASA.jpg|thumb|A NASA engineer sweeps an area with a corn broom to find the location of a hydrogen fire. Hydrogen burns with a nearly-invisible flame.]]Hydrogen poses a number of hazards to human safety, from potential [[Detonation|detonations]] and fires when mixed with air to being an [[Asphyxiant gas|asphyxiant]] in its pure, [[oxygen]]-free form.<ref name="NASAH2">{{cite web |author=Brown, W. J. |display-authors=etal |date=1997 |title=Safety Standard for Hydrogen and Hydrogen Systems |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19970033338.pdf |url-status=live |archive-url=https://web.archive.org/web/20170501105215/https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19970033338.pdf |archive-date=1 May 2017 |access-date=12 July 2017 |website=[[NASA]] |id=NSS 1740.16}}</ref> In addition, liquid hydrogen is a [[cryogen]] and presents dangers (such as [[frostbite]]) associated with very cold liquids.<ref>{{cite web |date=September 2004 |title=Liquid Hydrogen MSDS |url=http://www.hydrogenandfuelcellsafety.info/resources/mdss/Praxair-LH2.pdf |archive-url=https://web.archive.org/web/20080527233910/http://www.hydrogenandfuelcellsafety.info/resources/mdss/Praxair-LH2.pdf |archive-date=27 May 2008 |access-date=16 April 2008 |publisher=Praxair, Inc. |df=dmy-all}}</ref> Hydrogen dissolves in many metals and in addition to leaking out, may have adverse effects on them, such as [[hydrogen embrittlement]],<ref>{{cite journal |date=20 July 1985 |title='Bugs' and hydrogen embrittlement |journal=Science News |volume=128 |issue=3 |pages=41 |doi=10.2307/3970088 |jstor=3970088}}</ref> leading to cracks and explosions.<ref>{{cite web |last=Hayes |first=B. |title=Union Oil Amine Absorber Tower |url=http://www.twi.co.uk/content/oilgas_casedown29.html |archive-url=https://web.archive.org/web/20081120215355/http://www.twi.co.uk/content/oilgas_casedown29.html |archive-date=20 November 2008 |access-date=29 January 2010 |publisher=TWI}}</ref>

Hydrogen is flammable when mixed even in small amounts with ordinary air. Ignition can occur at a volumetric ratio of hydrogen to air as low as 4%.<ref>{{cite web |title=Hydrogen Safety |url=https://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/h2_safety_fsheet.pdf |publisher=Office of Energy Efficiency and Renewable Energy}}</ref> Moreover, hydrogen fire, while being extremely hot, is almost invisible, and thus can lead to accidental burns.<ref name="Cunn88">{{cite encyclopedia |title=Lactic acid to magnesium supply-demand relationships |encyclopedia=Encyclopedia of Chemical Processing and Design |publisher=Dekker |location=New York |url={{Google books|8erDL_DnsgAC|page=PA186|keywords=|text=|plainurl=yes}} |access-date=20 May 2015 |date=1988 |editor1=John J. McKetta |volume=28 |page=186 |isbn=978-0-8247-2478-8 |last2=Waltrip |first2=John S. |last3=Zanker |first3=Adam |last1=Walker |first1=James L. |editor2=William Aaron Cunningham}}</ref>

== Hydrogen infrastructure ==
{{Excerpt|Hydrogen infrastructure}}

=== Storage ===
{{Excerpt|Hydrogen storage}}

===Power plants===
{{See also|Hydrogen fuel cell power station|Natural hydrogen|Midcontinent Rift System}}
[[Prairie Island Nuclear Power Plant#Hydrogen production|Xcel Energy]] is going to build two [[Combined cycle hydrogen power plant|combined cycle power plants]] in the [[Midwestern United States|Midwest]] that can mix 30% hydrogen with the natural gas.<ref>{{Cite web |last=Orenstein |first=Walker |date=2024-02-01 |title=Xcel Energy wants to extend life of Prairie Island nuclear facility, add two gas plants |url=https://www.startribune.com/xcel-energy-long-term-plan-prairie-island-nuclear-gas-plants-wind-solar-large-scale-battery/600340390 |access-date=2024-08-14 |website=www.startribune.com |language=en}}</ref> [[Intermountain Power Plant]] is being retrofitted to a natural gas/hydrogen power plant that can run on 30% hydrogen as well, and is scheduled to run on pure hydrogen by 2045.<ref>{{Cite web |title=Chevron joins Mitsubishi in 300 GWh hydrogen storage project as construction continues |url=https://www.utilitydive.com/news/chevron-mitsubishi-hydrogen-storage-aces-delata-utah/693782/ |access-date=2024-08-14 |website=Utility Dive |language=en-US}}</ref>

== Costs ==
{{Update section|date=February 2024|reason=current prices need updating and white hydrogen adding}}
More widespread use of hydrogen in economies entails the need for investment and costs in its production, storage, distribution and use. Estimates of hydrogen's cost are therefore complex and need to make assumptions about the cost of energy inputs (typically gas and electricity), production plant and method (e.g. green or blue hydrogen), technologies used (e.g. [[Alkaline electrolysis|alkaline]] or [[Proton exchange membrane electrolysis|proton exchange membrane]] electrolysers), storage and distribution methods, and how different cost elements might change over time.<ref name=":4">{{Cite book |url=https://www.energy-transitions.org/publications/making-clean-hydrogen-possible/ |title=Making the Hydrogen Economy Possible: Accelerating Clean Hydrogen in an Electrified Economy |date=April 2021 |publisher=Energy Transitions Commission |page= |language=en-GB |access-date=2023-08-25}}</ref>{{Rp|page=|pages=49–65}} These factors are incorporated into calculations of the levelized costs of hydrogen (LCOH). The following table shows a range of estimates of the levelized costs of gray, blue, and green hydrogen, expressed in terms of US$ per kg of H2 (where data provided in other currencies or units, the average exchange rate to US dollars in the given year are used, and 1 kg of H2 is assumed to have a calorific value of 33.3kWh).
{|
|'''Production method'''
|'''Note'''
|'''Current cost (2020–2022)'''
|'''Projected 2030 cost'''
|'''Projected 2050 cost'''
|-
| colspan="5" |'''Gray hydrogen (not including a carbon tax)'''
|-
| rowspan="2" |[[International Energy Agency]]<ref name=":03">{{Cite book |url=https://www.iea.org/reports/global-hydrogen-review-2022 |title=Global Hydrogen Review 2022 |date=22 September 2022 |publisher=IEA |page=93 |language=en-GB |access-date=2023-08-25}}</ref>
| rowspan="2" |2022 costs estimated for June, when gas prices peaked in the wake of Russia's invasion of Ukraine
|2021: 1.0–2.5
| rowspan="2" | –
| rowspan="2" | –
|-
|2022: 4.8–7.8
|-
|[[PwC|PWC]]<ref name=":15">{{Cite web |last=PricewaterhouseCoopers |title=Green hydrogen economy – predicted development of tomorrow |url=https://www.pwc.com/gx/en/industries/energy-utilities-resources/future-energy/green-hydrogen-cost.html |access-date=2023-08-25 |website=PwC |language=en-gx}}</ref>
|
|2021: 1.2–2.4
|
|
|-
| colspan="5" |'''Blue hydrogen'''
|-
| rowspan="2" |International Energy Agency<ref name=":03" />
| rowspan="2" |2022 costs estimated for June, when gas prices peaked in the wake of Russia's invasion of Ukraine
|2021: 1.5–3.0
| rowspan="2" | –
| rowspan="2" | –
|-
|2022: 5.3–8.6
|-
|[[Department for Energy Security and Net Zero|UK government]]<ref name=":22">{{Cite web |title=Hydrogen Production Costs 2021 annex: Key assumptions and outputs for production technologies |url=https://www.gov.uk/government/publications/hydrogen-production-costs-2021 |access-date=2023-08-25 |website=GOV.UK |language=en}}</ref>
|Range dependent on gas price
|2020: 1.6–2.7
|1.6–2.7
|1.6–2.8
|-
|GEP<ref name=":3">{{Cite web |last=Saini |first=Anshuman |date=January 12, 2023 |title=Green & Blue Hydrogen: Current Levelized Cost of Production & Outlook {{!}} GEP Blogs |url=https://www.gep.com/blog/strategy/Green-and-blue-hydrogen-current-levelized-cost-of-production-and-outlook |access-date=2023-08-25 |website=www.gep.com |language=en}}</ref>
|
|2022: 2.8–3.5
|<nowiki>-</nowiki>
|<nowiki>-</nowiki>
|-
|[[Energy Transitions Commission]]<ref name=":4" />{{Rp|page=28}}
|
|2020: 1.5–2.4
|1.3–2.3
|1.4–2.2
|-
| colspan="5" |'''Green hydrogen'''
|-
| rowspan="2" |International Energy Agency<ref name=":03" />
| rowspan="2" |2030 and 2050 estimates are using solar power in regions with good solar conditions
|2021: 4.0–9.0
| rowspan="2" |<1.5
| rowspan="2" |<1.0
|-
|2022: 3.0-4.3
|-
| rowspan="2" |UK government<ref name=":22" />
|Using grid electricity, UK specific; range dependent on electricity price, and electrolyser technology and cost
|2020: 4.9–7.9
|4.4–6.6
|4.0–6.3
|-
|Using otherwise curtailed renewable electricity, UK specific; range dependent on electrolyser technology and cost
|2020: 2.4–7.9
|1.7–5.6
|1.5–4.6
|-
|[[International Renewable Energy Agency|IRENA]]<ref>IRENA (2020), [https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2020/Dec/IRENA_Green_hydrogen_cost_2020.pdf Green Hydrogen Cost Reduction: Scaling up Electrolysers to Meet the 1.5 °C Climate Goal], International Renewable Energy Agency, Abu Dhabi, p. 91.</ref>
|
|2020: 2.2–5.2
|1.4–4.1
|1.1–3.4
|-
|GEP<ref name=":3" />
|Source notes green H2 production cost has fallen by 60% since 2010
|2022: 3.0–6.0
|
|
|-
|[[Lazard]]<ref>{{Cite book |url=https://www.lazard.com/research-insights/2023-levelized-cost-of-energyplus/ |title=2023 Levelized Cost Of Energy+ |date=April 12, 2023 |publisher=Lazard |page=27 |language=en |access-date=2023-08-25}}</ref>
|
|2022: 2.8–5.3
|
|
|-
|PWC<ref name=":15" />
|
|2021: 3.5–9.5
|1.8–4.8
|1.2–2.4
|-
|Energy Transitions Commission<ref name=":4" />{{Rp|page=28}}
|
|2020: 2.6–3.6
|1.0–1.7
|0.7–1.2
|}
The range of cost estimates for commercially available hydrogen production methods is broad, As of 2022, gray hydrogen is cheapest to produce without a tax on its CO2 emissions, followed by blue and green hydrogen. Blue hydrogen production costs are not anticipated to fall substantially by 2050,<ref name=":22" /><ref name=":4" />{{Rp|page=28}} can be expected to fluctuate with natural gas prices and could face [[carbon tax]]es for uncaptured emissions.<ref name=":4" />{{Rp|page=79}} The cost of [[Electrolysis|electrolysers]] fell by 60% from 2010 to 2022,<ref name=":3" /> before rising slightly due to an increasing [[cost of capital]].<ref name=":1" /> Their cost is projected to fall significantly to 2030 and 2050,<ref name=":52">{{Cite book |last1=Patonia |first1=Aliaksei |url=https://www.oxfordenergy.org/publications/cost-competitive-green-hydrogen-how-to-lower-the-cost-of-electrolysers/ |title=Cost-competitive green hydrogen: how to lower the cost of electrolysers? |last2=Poudineh |first2=Rahmat |date=January 2022 |publisher=Oxford Institute for Energy Studies |page= |language=en |access-date=2023-08-25}}</ref>{{Rp|page=26}} driving down the cost of green hydrogen alongside the falling cost of renewable power generation.<ref>{{Cite journal |last=Roser |first=Max |date=2023-09-01 |title=Why did renewables become so cheap so fast? |url=https://ourworldindata.org/cheap-renewables-growth |journal=Our World in Data}}</ref><ref name=":4" />{{Rp|page=28}} It is cheapest to produce green hydrogen with surplus renewable power that would otherwise be [[Curtailment (electricity)|curtailed]], which favors electrolyzers capable of responding to low and [[Variable renewable energy|variable power levels]].<ref name=":52" />{{Rp|page=5}}

A 2022 [[Goldman Sachs]] analysis anticipates that globally green hydrogen will achieve cost parity with grey hydrogen by 2030, earlier if a global carbon tax is placed on gray hydrogen.<ref name="Goldman Sachs Research 4–6"/> In terms of cost per unit of energy, blue and gray hydrogen will always cost more than the fossil fuels used in its production, while green hydrogen will always cost more than the renewable electricity used to make it.

Subsidies for clean hydrogen production are much higher in the US and EU than in India.<ref>{{Cite web |last=Martin |first=Polly |date=2023-06-29 |title=India to offer green hydrogen production subsidy of up to $0.60/kg — for three years only |url=https://www.hydrogeninsight.com/production/india-to-offer-green-hydrogen-production-subsidy-of-up-to-0-60-kg-for-three-years-only/2-1-1477425 |access-date=2023-09-26 |website=Hydrogen news and intelligence {{!}} Hydrogen Insight |language=en}}</ref>

== Examples and pilot programs ==
{{Update|section|date=February 2019}}

[[File:Brno, Autotec, Mercedes Citaro na palivové články II.jpg|thumb|A [[Mercedes-Benz O530 Citaro]] powered by hydrogen fuel cells in [[Brno]], Czech Republic]]

The distribution of hydrogen for the purpose of transportation is being tested around the world, particularly in the US ([[California Hydrogen Highway|California]], [[Massachusetts Fuel Cell Bus Project|Massachusetts]]), [[BC hydrogen highway|Canada]], [[Japan hydrogen fuel cell project|Japan]], the EU ([[Portugal]], [[Hynor|Norway]], Denmark, [[Germany]]), and [[Iceland]].

An indicator of the presence of large natural gas infrastructures already in place in countries and in use by citizens is the number of natural gas vehicles present in the country. The countries with the largest amount of natural gas vehicles are (in order of magnitude):<ref>{{Cite web |title=Worldwide NGV statistics |url=http://www.ngvjournal.com/worldwide-ngv-statistics/ |url-status=live |archive-url=https://web.archive.org/web/20150206153839/http://www.ngvjournal.com/worldwide-ngv-statistics/ |archive-date=2015-02-06 |access-date=2019-09-29}}</ref>
[[Iran]], [[China]], [[Pakistan]], [[Argentina]], [[India]], [[Brazil]], [[Italy]], [[Colombia]], [[Thailand]], [[Uzbekistan]], [[Bolivia]], [[Armenia]], [[Bangladesh]], [[Egypt]], [[Peru]], [[Ukraine]], the [[United States]]. Natural gas vehicles can also be [[Hydrogen internal combustion engine vehicle#Adaptation of existing engines|converted to run on hydrogen]].

Also, in a few private homes, [[Micro combined heat and power#Fuel cells|fuel cell micro-CHP]] plants can be found, which can operate on hydrogen, or other fuels as natural gas or LPG.<ref>{{Cite web |title=Fuel Cell micro CHP |url=http://www.pace-energy.eu/micro-cogeneration/ |url-status=live |archive-url=https://web.archive.org/web/20191106175546/http://www.pace-energy.eu/micro-cogeneration/ |archive-date=2019-11-06 |access-date=2019-10-23}}</ref><ref>{{Cite web |title=Fuel cell micro Cogeneration |url=https://www.cogeneurope.eu/events/past-events/cogen-event/fuel-cell-micro-cogeneration-generating-sustainable-heat-and-power-for-your-home |url-status=live |archive-url=https://web.archive.org/web/20191023131059/https://www.cogeneurope.eu/events/past-events/cogen-event/fuel-cell-micro-cogeneration-generating-sustainable-heat-and-power-for-your-home |archive-date=2019-10-23 |access-date=2019-10-23}}</ref>

=== Australia ===
Western [[Australia]]'s Department of Planning and Infrastructure operated three Daimler Chrysler Citaro fuel cell buses as part of its Sustainable Transport Energy for Perth Fuel Cells Bus Trial in Perth.<ref>{{cite web |date=13 April 2007 |title=Perth Fuel Cell Bus Trial |url=http://www.dpi.wa.gov.au/ecobus/1206.asp |url-status=dead |archive-url=https://web.archive.org/web/20080607172715/http://www.dpi.wa.gov.au/ecobus/1206.asp |archive-date=7 June 2008 |access-date=2008-05-09 |publisher=Department for Planning and Infrastructure, Government of [[Western Australia]]}}</ref> The buses were operated by Path Transit on regular Transperth public bus routes. The trial began in September 2004 and concluded in September 2007. The buses' fuel cells used a proton exchange membrane system and were supplied with raw hydrogen from a BP refinery in Kwinana, south of Perth. The hydrogen was a byproduct of the refinery's industrial process. The buses were refueled at a station in the northern Perth suburb of Malaga.

In October 2021, [[Queensland]] Premier [[Annastacia Palaszczuk]] and [[Andrew Forrest]] announced that Queensland will be home to the world's largest hydrogen plant.<ref>{{Cite news |date=October 11, 2021 |title='Green industrial revolution': Queensland announces plans to mass produce green ammonia |newspaper=ABC News |url=https://www.abc.net.au/news/2021-10-11/queensland-hydrogen-twiggy-forrest-ammonia-feasiblity/100528732 |url-status=live |access-date=2021-10-12 |archive-url=https://web.archive.org/web/20211012192350/https://www.abc.net.au/news/2021-10-11/queensland-hydrogen-twiggy-forrest-ammonia-feasiblity/100528732 |archive-date=2021-10-12 |via=abc.net.au}}</ref>

In Australia, the [[Australian Renewable Energy Agency|Australian Renewable Energy Agency (ARENA)]] has invested $55 million in 28 hydrogen projects, from early stage research and development to early stage trials and deployments. The agency's stated goal is to produce hydrogen by electrolysis for $2 per kilogram, announced by Minister for Energy and Emissions Angus Taylor in a 2021 Low Emissions Technology Statement.<ref>{{Cite web |date=30 November 2020 |title=Australia's pathway to $2 per kg hydrogen – ARENAWIRE |url=https://arena.gov.au/blog/australias-pathway-to-2-per-kg-hydrogen/ |url-status=live |archive-url=https://web.archive.org/web/20201215065859/https://arena.gov.au/blog/australias-pathway-to-2-per-kg-hydrogen/ |archive-date=2020-12-15 |access-date=2021-01-06 |website=Australian Renewable Energy Agency}}</ref>

=== European Union ===
Countries in the [[EU]] which have a relatively large natural gas pipeline system already in place include [[Belgium]], [[Germany]], [[France]], and the [[Netherlands]].<ref name="Hydrogen transport & distribution">{{Cite web |title=Hydrogen transport & distribution |url=https://hydrogeneurope.eu/hydrogen-transport-distribution |url-status=live |archive-url=https://web.archive.org/web/20190929110509/https://hydrogeneurope.eu/hydrogen-transport-distribution |archive-date=2019-09-29 |access-date=2019-09-29}}</ref> In 2020, The EU launched its European Clean Hydrogen Alliance (ECHA).<ref>{{Cite web |last=Pollet |first=Mathieu |date=2020 |title=AExplainer: Why is the EU Commission betting on hydrogen for a greener future? |url=https://www.euronews.com/2020/07/10/explainer-why-is-the-eu-commission-betting-on-hydrogen-for-a-cleaner-future |url-status=live |archive-url=https://web.archive.org/web/20200807130615/https://www.euronews.com/2020/07/10/explainer-why-is-the-eu-commission-betting-on-hydrogen-for-a-cleaner-future |archive-date=2020-08-07 |access-date=2020-08-14 |website=euronews}}</ref><ref>{{Cite web |title=ECHA |url=https://ec.europa.eu/growth/industry/policy/european-clean-hydrogen-alliance_en |url-status=live |archive-url=https://web.archive.org/web/20200812182627/https://ec.europa.eu/growth/industry/policy/european-clean-hydrogen-alliance_en |archive-date=2020-08-12 |access-date=2020-08-14}}</ref>

==== France ====
Green hydrogen has become more common in France. A €150 million Green Hydrogen Plan was established in 2019, and it calls for building the infrastructure necessary to create, store, and distribute hydrogen as well as using the fuel to power local transportation systems like buses and trains. Corridor H2, a similar initiative, will create a network of hydrogen distribution facilities in [[Occitania]] along the route between the Mediterranean and the North Sea. The Corridor H2 project will get a €40 million loan from the [[European Investment Bank|EIB]].<ref name=":77">{{Cite web |title=French port bets big on floating wind farms planned in Mediterranean |url=https://www.eib.org/en/essays/floating-wind-farms |access-date=2022-09-26 |website=European Investment Bank}}</ref><ref>{{Cite web |date=23 June 2022 |title=Green Hydrogen: A key investment for the energy transition |url=https://blogs.worldbank.org/ppps/green-hydrogen-key-investment-energy-transition |access-date=2022-09-26 |website=blogs.worldbank.org}}</ref>

==== Germany ====
German car manufacturer [[BMW]] has been working with hydrogen for years.{{quantify|date=October 2021}}.<ref>{{Cite web |date=24 October 2007 |title=E3B1C256-BFCB-4CEF-88A6-1DCCD7666635 |url=https://www.scmp.com/article/612717/test-drive-bmws-car-future-its-gas |url-status=live |archive-url=https://web.archive.org/web/20211029174424/https://www.scmp.com/article/612717/test-drive-bmws-car-future-its-gas |archive-date=2021-10-29 |access-date=2021-10-12}}</ref>
The German government has announced plans to hold tenders for 5.5 GW of new hydrogen-ready gas-fired power plants and 2 GW of "comprehensive H2-ready modernisations" of existing gas power stations at the end of 2024 or beginning of 2025<ref>{{cite web | url=https://www.hydrogeninsight.com/power/germany-to-tender-for-5-5gw-of-new-hydrogen-ready-gas-fired-power-plants-and-2gw-of-conversions/2-1-1674082 | title=Germany to tender for 5.5GW of new hydrogen-ready gas-fired power plants and 2GW of conversions | date=8 July 2024 }}</ref>

==== Iceland ====
[[Iceland]] has committed to becoming the world's first hydrogen economy by the year 2050.<ref>{{cite web |last=Hannesson |first=Hjálmar W. |date=2007-08-02 |title=Climate change as a global challenge |url=http://www.mfa.is/speeches-and-articles/nr/3800 |url-status=live |archive-url=https://web.archive.org/web/20140107205851/http://www.mfa.is/news-and-publications/nr/3800 |archive-date=2014-01-07 |access-date=2008-05-09 |publisher=[[Iceland]] [[Minister for Foreign Affairs of Iceland|Ministry for Foreign Affairs]]}}</ref> Iceland is in a unique position. Presently,{{when|date=June 2019}} it imports all the petroleum products necessary to power its automobiles and [[fishing fleet]]. Iceland has large geothermal resources, so much that the local price of electricity actually is ''lower'' than the price of the hydrocarbons that could be used to produce that electricity.

Iceland already converts its surplus electricity into exportable goods and hydrocarbon replacements. In 2002, it produced 2,000 tons of hydrogen gas by electrolysis, primarily for the production of [[anhydrous ammonia|ammonia]] (NH3) for fertilizer. Ammonia is produced, transported, and used throughout the world, and 90% of the cost of ammonia is the cost of the energy to produce it.

Neither industry directly replaces hydrocarbons. [[Reykjavík]], Iceland, had a small pilot fleet of city buses running on compressed hydrogen,<ref name="detnews">{{cite news |last=Doyle |first=Alister |date=January 14, 2005 |title=Iceland's hydrogen buses zip toward oil-free economy |agency=Reuters |url=http://www.detnews.com/2005/autosinsider/0501/14/autos-60181.htm |url-status=dead |access-date=2008-05-09 |archive-url=https://archive.today/20120724042846/http://www.detnews.com/2005/autosinsider/0501/14/autos-60181.htm |archive-date=July 24, 2012}}</ref> and research on powering the nation's fishing fleet with hydrogen is under way (for example by companies as [[Icelandic New Energy]]). For more practical purposes, Iceland might process imported oil with hydrogen to extend it, rather than to replace it altogether.

The Reykjavík buses are part of a larger program, HyFLEET:CUTE,<ref>{{cite web |title=What is HyFLEET:CUTE? |url=http://www.global-hydrogen-bus-platform.com/index.php |url-status=dead |archive-url=https://web.archive.org/web/20080224165308/http://www.global-hydrogen-bus-platform.com/index.php |archive-date=2008-02-24 |access-date=2008-05-09}}</ref> operating hydrogen fueled buses in eight European cities. HyFLEET:CUTE buses were also operated in Beijing, China and Perth, Australia (see below). A pilot project demonstrating a hydrogen economy is operational on the [[Norway|Norwegian]] island of [[Utsira]]. The installation combines wind power and hydrogen power. In periods when there is surplus wind energy, the excess power is used for generating hydrogen by [[electrolysis]]. The hydrogen is stored, and is available for power generation in periods when there is little wind.{{citation needed|date=December 2011}}

=== India ===
[[India]] is said to adopt hydrogen and H-CNG, due to several reasons, amongst which the fact that a national rollout of natural gas networks is already taking place and natural gas is already a major vehicle fuel. In addition, India suffers from extreme air pollution in urban areas.<ref>{{Cite web |title=Hydrogen vehicles and refueling infrastructure in India |url=https://www.energy.gov/sites/prod/files/2014/03/f10/cng_h2_workshop_11_das.pdf |url-status=live |archive-url=https://web.archive.org/web/20170612130231/https://energy.gov/sites/prod/files/2014/03/f10/cng_h2_workshop_11_das.pdf |archive-date=2017-06-12 |access-date=2019-09-28}}</ref><ref>{{cite journal |last1=Das |first1=L |date=1991 |title=Exhaust emission characterization of hydrogen-operated engine system: Nature of pollutants and their control techniques |journal=International Journal of Hydrogen Energy |volume=16 |issue=11 |pages=765–775 |doi=10.1016/0360-3199(91)90075-T|bibcode=1991IJHE...16..765D }}</ref> According to some estimates, nearly 80% of India's hydrogen is projected to be green, driven by cost declines and new production technologies.<ref>{{Cite web|url=https://www.bridgeindia.org.uk/wp-content/uploads/2021/03/Bridge-India-UK-India-Energy-Report-2021.pdf|title=UK-India Energy Collaborations report}}</ref>

Currently however, hydrogen energy is just at the Research, Development and Demonstration (RD&D) stage.<ref>{{Cite web |title=MNRE: FAQ |url=https://mnre.gov.in/file-manager/UserFiles/faq_hydrogenenergy.htm |url-status=live |archive-url=https://web.archive.org/web/20190921111217/https://mnre.gov.in/file-manager/UserFiles/faq_hydrogenenergy.htm |archive-date=2019-09-21 |access-date=2019-09-28}}</ref><ref>[https://web.archive.org/web/20120927155111/http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/cng_h2_workshop_9_chenoy.pdf Overview of Indian Hydrogen Programme]</ref> As a result, the number of hydrogen stations may still be low,<ref>{{Cite web |title=H2 stations worldwide |url=https://www.netinform.net/h2/h2stations/h2stations.aspx |url-status=live |archive-url=https://web.archive.org/web/20190921111217/https://www.netinform.net/h2/h2stations/h2stations.aspx |archive-date=2019-09-21 |access-date=2019-09-28}}</ref> although much more are expected to be introduced soon.<ref>{{Cite web |date=23 February 2016 |title=India working on more H2 stations |url=https://www.gasworld.com/india-working-on-hydrogen-fuel-stations/2010006.article |url-status=live |archive-url=https://web.archive.org/web/20190921111210/https://www.gasworld.com/india-working-on-hydrogen-fuel-stations/2010006.article |archive-date=2019-09-21 |access-date=2019-09-28}}</ref><ref>{{Cite news |title=Shell plans to open 1200 fuel stations in India, some of which may include H2 refilling |newspaper=The Economic Times |url=https://economictimes.indiatimes.com/industry/energy/oil-gas/shell-plans-opening-1200-retail-stations-in-india-in-10-years/articleshow/65660768.cms |url-status=live |access-date=2019-09-28 |archive-url=https://web.archive.org/web/20190922161455/https://economictimes.indiatimes.com/industry/energy/oil-gas/shell-plans-opening-1200-retail-stations-in-india-in-10-years/articleshow/65660768.cms |archive-date=2019-09-22}}</ref><ref>{{Cite web |title=Hydrogen Vehicles and Refueling Infrastructure in India |url=https://www.energy.gov/sites/prod/files/2014/03/f10/cng_h2_workshop_11_das.pdf |url-status=live |archive-url=https://web.archive.org/web/20170612130231/https://energy.gov/sites/prod/files/2014/03/f10/cng_h2_workshop_11_das.pdf |archive-date=2017-06-12 |access-date=2019-09-28}}</ref>

=== Poland ===
It planning open first hydrogen publication stations, The Ministry of Climate and Environment (MKiŚ) will soon schan competitions for 2-3 hydrogen refueling stations, Polish Deputy Minister in this ministry Krzysztof Bolesta.<ref>{{cite web | url=https://hydrogen-central.com/orlen-hydrogen-refueling-stations-poland/ | title=ORLEN will Build the First Hydrogen Refueling Stations in Poland | date=6 May 2021 }}</ref>

=== Saudi Arabia ===
Saudi Arabia as a part of the [[Neom|NEOM project]], is looking to produce roughly 1.2 million tonnes of green ammonia a year, beginning production in 2025.<ref>{{Cite web |date=21 April 2021 |title=Saudi Arabia's $5bn green hydrogen-based ammonia plant to begin production in 2025 |url=https://energy-utilities.com/saudi-arabia-s-5bn-green-hydrogenbased-ammonia-news111872.html |access-date=2022-01-13 |website=Energy & Utilities |archive-date=2021-04-21 |archive-url=https://web.archive.org/web/20210421122019/https://energy-utilities.com/saudi-arabia-s-5bn-green-hydrogenbased-ammonia-news111872.html |url-status=dead }}</ref>

In Cairo, Egypt, Saudi real estate funding skyscraper project powered by hydrogen.<ref>https://www.reuters.com/sustainability/saudi-firm-plans-hydrogen-powered-skyscraper-egypts-new-capital-2024-08-14/ {{Bare URL inline|date=August 2024}}</ref>

=== Turkey ===
The [[Ministry of Energy and Natural Resources (Turkey)|Turkish Ministry of Energy and Natural Resources]] and the [[UNIDO|United Nations Industrial Development Organization]] created the [[International Centre for Hydrogen Energy Technologies]] (UNIDO-ICHET) in [[Istanbul]] in 2004 and it ran to 2012.<ref>{{cite web |date=31 August 2009 |title=Independent Mid-Term Review of the UNIDO Project: Establishment and operation of the International Centre for Hydrogen Energy Technologies (ICHET), TF/INT/03/002 |url=http://www.unido.org/fileadmin/user_media/About_UNIDO/Evaluation/TORs/TOR%20ICHET%20final.PDF |url-status=dead |archive-url=https://web.archive.org/web/20100601075325/http://www.unido.org/fileadmin/user_media/About_UNIDO/Evaluation/TORs/TOR%20ICHET%20final.PDF |archive-date=1 June 2010 |access-date=2010-07-20 |publisher=[[UNIDO]] |df=dmy-all}}</ref> In 2023 the ministry published a Hydrogen Technologies Strategy and Roadmap.<ref>{{Cite web |title=Announcement – Republic of Türkiye Ministry of Energy and Natural Resources |url=https://enerji.gov.tr/announcements-detail?id=20349 |access-date=2024-02-14 |website=enerji.gov.tr}}</ref>

=== United Kingdom ===
The [[United Kingdom|UK]] started a fuel cell pilot program in January 2004, the program ran two Fuel cell buses on route 25 in [[London]] until December 2005, and switched to route RV1 until January 2007.<ref>{{cite web | url= http://www.tfl.gov.uk/corporate/projectsandschemes/environment/2017.aspx#routes | title= Hydrogen buses |publisher= Transport for London | access-date= 2008-05-09 |archive-url = https://web.archive.org/web/20080323064054/http://www.tfl.gov.uk/corporate/projectsandschemes/environment/2017.aspx#routes |archive-date = March 23, 2008}}</ref> The Hydrogen Expedition is currently working to create a hydrogen fuel cell-powered ship and using it to circumnavigate the globe, as a way to demonstrate the capability of hydrogen fuel cells.<ref>{{cite web | url= http://www.atti-info.org/HydrogenVeh/prospectus.pdf | title= The Hydrogen Expedition | date= January 2005 | access-date= 2008-05-09 | url-status= dead | archive-url= https://web.archive.org/web/20080527234233/http://www.atti-info.org/HydrogenVeh/prospectus.pdf | archive-date= 2008-05-27 }}</ref> In August 2021 the UK Government claimed it was the first to have a Hydrogen Strategy and produced a document.<ref>{{Cite web|date=August 2021|title=UK Hydrogen Strategy|url=https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1011283/UK-Hydrogen-Strategy_web.pdf|url-status=live|website=UK Government|access-date=2021-08-19|archive-date=2021-08-19|archive-url=https://web.archive.org/web/20210819205309/https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1011283/UK-Hydrogen-Strategy_web.pdf}}</ref>

In August 2021, Chris Jackson quit as chair of the UK Hydrogen and Fuel Cell Association, a leading hydrogen industry association, claiming that UK and Norwegian oil companies had intentionally inflated their cost projections for blue hydrogen in order to maximize future [[transfer payment|technology support payments]] by the UK government.<ref name="ambrose-2021">{{cite news |last1=Ambrose |first1=Jillian |date=20 August 2021 |title=Oil firms made 'false claims' on blue hydrogen costs, says ex-lobby boss |work=The Guardian |location=London, United Kingdom |url=http://www.theguardian.com/environment/2021/aug/20/oil-firms-made-false-claims-on-blue-hydrogen-costs-says-ex-lobby-boss |url-status=live |access-date=2021-08-24 |archive-url=https://web.archive.org/web/20210824075238/https://www.theguardian.com/environment/2021/aug/20/oil-firms-made-false-claims-on-blue-hydrogen-costs-says-ex-lobby-boss |archive-date=2021-08-24 |issn=0261-3077}}</ref>

=== United States ===

Several domestic [[Automotive industry in the United States|U.S. automobile companies]] have developed vehicles using hydrogen, such as GM and Toyota.<ref>{{Cite web |title=Are hydrogen fuel cell vehicles the future of autos? |url=https://abcnews.go.com/Business/hydrogen-fuel-cell-vehicles-future-autos/story?id=74583475 |url-status=live |archive-url=https://web.archive.org/web/20210117010939/https://abcnews.go.com/Business/hydrogen-fuel-cell-vehicles-future-autos/story?id=74583475 |archive-date=2021-01-17 |access-date=2021-01-18 |website=ABC News}}</ref> However, as of February 2020, infrastructure for hydrogen was underdeveloped except in some parts of California.<ref>{{Cite news |last=Siddiqui |first=Faiz |title=The plug-in electric car is having its moment. But despite false starts, Toyota is still trying to make the fuel cell happen.|newspaper=Washington Post |url=https://www.washingtonpost.com/technology/2020/02/26/hydrogen-fuel-cell-cars/ |url-status=live |access-date=2021-01-18 |archive-url=https://web.archive.org/web/20210119142059/https://www.washingtonpost.com/technology/2020/02/26/hydrogen-fuel-cell-cars/ |archive-date=2021-01-19 |issn=0190-8286}}</ref> The [[United States]] have their own [[United States Hydrogen Policy|hydrogen policy]].{{citation needed|date=June 2019}} A joint venture between [[NREL]] and [[Xcel Energy]] is combining wind power and hydrogen power in the same way in Colorado.<ref>{{cite web |date=January 8, 2007 |title=Experimental 'wind to hydrogen' system up and running |url=http://www.physorg.com/news87494382.html |url-status=live |archive-url=https://web.archive.org/web/20130126092957/http://phys.org/news87494382.html |archive-date=2013-01-26 |access-date=2008-05-09 |publisher=Physorg.com}}</ref> [[Newfoundland and Labrador Hydro|Hydro]] in [[Newfoundland and Labrador]] are converting the current [[Wind-Diesel Hybrid Power Systems|wind-diesel Power System]] on the remote island of [[Ramea]] into a [[Wind-Hydrogen Hybrid Power Systems]] facility.<ref>{{cite web |date=May 16, 2006 |title=Hydrogen Engine Center Receives Order for Hydrogen Power Generator 250kW Generator for Wind/Hydrogen Demonstration |url=http://www.hydrogenenginecenter.com/userdocs/NRCan_Press_Release_Final_05.16.06.pdf |url-status=dead |archive-url=https://web.archive.org/web/20080527234233/http://www.hydrogenenginecenter.com/userdocs/NRCan_Press_Release_Final_05.16.06.pdf |archive-date=May 27, 2008 |access-date=2008-05-09 |publisher=Hydrogen Engine Center, Inc.}}</ref> Five pump station hubs being delivered to heavy-duty H2 trucks in Texas.<ref>{{Cite web |last=Kilgore |first=Erin |date=2024-01-12 |title=Texas Hydrogen Stations Infrastructure Gets Boost From Biden Administration |url=https://www.hydrogenfuelnews.com/hydrogen-stations-texas/8562318/ |website=Hydrogen Fuel News}}</ref> Hydrogen City built Green by Hydrogen International (GHI), to planning open in 2026.<ref>{{Cite web |date=2022-03-08 |title=World's largest green H2 hub, Hydrogen City, to open in Texas in 2026 |url=https://newatlas.com/energy/worlds-largest-green-hydrogen-city/ |first=Loz |last=Blain |website=New Atlas}}</ref>

In 2006, Florida’s infrastructure project was commissioned.<ref>{{Cite web |date=April 12, 2007 |title=The Florida Hydrogen Initiative |url=https://www.hydrogen.energy.gov/docs/hydrogenprogramlibraries/pdfs/review07/tvp_11_levine.pdf?sfvrsn=3534d200_1 |website=Hydrogen Program}}</ref> First opened Orlando as public bus transportation, Ford Motor Company announced putting a fleet of hydrogen-fueled Ford E-450.<ref>{{Cite web |title=First Hydrogen Station Opens |url=https://www.tampabay.com/archive/2007/05/24/first-hydrogen-station-opens/ |date=May 24, 2007 |website=Tampa Bay Times|url-status=live |archive-url=https://web.archive.org/web/20240709025342/https://www.tampabay.com/archive/2007/05/24/first-hydrogen-station-opens/ |archive-date= 2024-07-09}}</ref><ref>{{Cite web |date=23 May 2007 |title=Florida gets hydrogen-fueled buses |url=https://www.drive.com.au/news/florida-gets-hydrogenfueled-buses-20070523-1413y/ |url-status=live |archive-url=https://web.archive.org/web/20240709014134/https://www.drive.com.au/news/florida-gets-hydrogenfueled-buses-20070523-1413y/ |archive-date=2024-07-09 |website=Drive}}</ref> Liquidated hydrogen mobile system was constructed at Titusville.<ref>{{Cite web |last=Himmelstein |first=S. |date=January 18, 2023 |title=Liquid hydrogen system is compact and mobile |url=https://insights.globalspec.com/article/19790/liquid-hydrogen-system-is-compact-and-mobile |url-status=live |archive-url=https://web.archive.org/web/20240709020150/https://insights.globalspec.com/article/19790/liquid-hydrogen-system-is-compact-and-mobile |archive-date=2024-07-09 |website=GlobalSpec}}</ref><ref>{{Cite web |date=2023-02-24 |title=GENH2 Partners with H2 GENESIS to Provide Small-Scale Hydrogen Liquefaction |url=https://hydrogen-central.com/genh2-partners-h2-genesis-to-provide-small-scale-hydrogen-liquefaction/ |website=Hydrogen Central|url-status=live |archive-url=https://web.archive.org/web/20240709000122/https://hydrogen-central.com/genh2-partners-h2-genesis-to-provide-small-scale-hydrogen-liquefaction/ |archive-date= 2024-07-09 }}</ref> An FPL’s pilot clean hydrogen facility operated in Okeechobee County.<ref>{{Cite web |last1=Kurzner |first1=Jeff |first2=Nikki |last2=Cabus |date=2024-02-28 |title=FPL announces completion of Florida's first ever clean hydrogen hub of its kind |url=https://techhubsouthflorida.org/fpl-announces-completion-of-florida-first-ever-clean-hydrogen-hub-of-its-kind/ |website=South Florida Tech Hub|url-status=live |archive-url=https://web.archive.org/web/20240709014526/https://techhubsouthflorida.org/fpl-announces-completion-of-florida-first-ever-clean-hydrogen-hub-of-its-kind/ |archive-date= 2024-07-09}}</ref>

A similar pilot project on [[Stuart Island (Washington)|Stuart Island]] uses [[solar power]], instead of [[wind power]], to generate electricity. When excess electricity is available after the batteries are fully charged, hydrogen is generated by electrolysis and stored for later production of electricity by fuel cell.<ref>{{cite web |title=Stuart Island Energy Initiative |url=http://www.siei.org |website=siei.org |url-status=live |archive-url=https://web.archive.org/web/20130618081052/http://siei.org/ |archive-date=2013-06-18 |access-date=2008-05-09}}</ref> The US also have a large natural gas pipeline system already in place.<ref name="Hydrogen transport & distribution" />

=== Vietnam ===
Việt Nam Energy Association have included green hydrogenation support.<ref>{{Cite web |title=Hydrogen production project promotes green energy transition in Việt Nam |url=https://vietnamnews.vn/economy/1068281/hydrogen-production-project-promotes-green-energy-transition-in-viet-nam.html |access-date=2024-08-14 |website=vietnamnews.vn}}</ref> Australian clean energy company Pure Hydrogen Corporation Limited announced on July 22 that it has signed an MoU with Vietnam public transportation.<ref>https://news.finclear.tradecentre.io/asx/document/20240722/02830030.pdf {{Bare URL PDF|date=August 2024}}</ref>

== See also ==
{{colbegin}}
* [[Alternative fuel]]
* [[Biohydrogen]]
* [[Combined cycle hydrogen power plant]]
* [[Energy development]]
* [[Hydrogen damage]]
* [[Hydrogen fuel cell power plant]]
* [[Hydrogen internal combustion engine vehicle]]
* [[Hydrogen-powered aircraft]]
* [[Hydrogen-powered ship]]
* [[Hydrogen prize]]
* [[Hydrogen tanker]]
* [[Hydrogen train]]
* [[Lolland Hydrogen Community]]
* [[Methane pyrolysis]]
* [[Timeline of sustainable energy research 2020–present#Hydrogen energy]]

{{colend}}
{{Portalbar|Chemistry|Energy|Science}}

==References==
{{reflist|refs=
<ref name="Hydrogen production :2">{{Cite web |last=Deign |first=Jason |date=2020-06-29 |title=So, What Exactly Is Green Hydrogen? |url=https://www.greentechmedia.com/articles/read/green-hydrogen-explained |url-status=live |archive-url=https://web.archive.org/web/20220323195427/https://www.greentechmedia.com/articles/read/green-hydrogen-explained |archive-date=2022-03-23 |access-date=2022-02-11 |website=Greentechmedia}}</ref>}}

===Sources===
*{{cite book |ref = {{harvid|UKCCC H2|2018}}
|publisher = UK [[Committee on Climate Change]]
|title = Hydrogen in a low-carbon economy
|year = 2018
|url = https://www.theccc.org.uk/wp-content/uploads/2018/11/Hydrogen-in-a-low-carbon-economy.pdf
}}

*{{cite book |ref = {{harvid|IEA H2|2019}}
| publisher=[[International Energy Agency]]
| title=The Future of Hydrogen
| year=2019
| url-access=registration
| url=https://www.iea.org/reports/the-future-of-hydrogen
}}

==External links==
{{Commons}}
{{wikiquote}}
* [http://www.iphe.net/ International Partnership for the Hydrogen Economy]
* [https://www.iea.org/reports/hydrogen Hydrogen]. International Energy Agency. 2022
* [http://www.h2euro.org/ European Hydrogen Association]
* [https://model.energy/products/ Online calculator for green hydrogen production and transport costs]

{{emerging technologies|energy=yes}}
{{Alternative propulsion}}

{{DEFAULTSORT:Hydrogen Economy}}
[[Category:Fuel technology]]
[[Category:Hydrogen economy]]
[[Category:Hydrogen technologies]]
[[Category:Industrial gases]]
[[Category:Low-carbon economy]]