Gold — Mediated Wiki

{{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}}{{Use American English|date=May 2025}}

'''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-metallic-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, with only platinum ranked as less reactive.<ref>{{Cite web |title=The reactivity series of metals - Reactions of metals - AQA - GCSE Combined Science Revision - AQA Trilogy |url=https://www.bbc.co.uk/bitesize/guides/zy7dgdm/revision/1 |access-date=2025-07-02 |website=BBC Bitesize |language=en-GB |archive-date=2 July 2025 |archive-url=https://web.archive.org/web/20250702022949/https://www.bbc.co.uk/bitesize/guides/zy7dgdm/revision/1 |url-status=dead }}</ref> Gold is solid under standard conditions.

Gold often occurs as the free element (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 such as copper, platinum, and palladium, as well as 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 when compared to silver<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> (though thirty times more common than platinum),<ref>{{Cite web |last=Lee |first=Jinjoo |title=Costco Members Are Buying Platinum. Should You? |url=https://www.wsj.com/finance/commodities-futures/costco-members-are-buying-platinum-should-you-0b532204 |access-date=2025-06-24 |website=WSJ |date=14 October 2024 |language=en-US}}</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. Most 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|website=World Gold Council}}</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 |website=World Gold Council|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. Auranofin is a gold-containing drug used to treat rheumatoid arthritis.

== Etymology == [[File:Beowulf - gold.jpg|thumb|left|The word ''gold'' in the ''Beowulf'' manuscript]] ''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>

== Characteristics == [[File:Small gold nugget 5mm dia and corresponding foil surface of half sq meter.jpg|thumb|upright|left|A {{convert|5|mm|abbr=on|sp=us}} gold nugget (dot in front of frame) can be hammered into a gold foil of about {{convert|0.5|m2|abbr=on|sp=us}} in area.]] Gold is the most malleable metal. 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 |article-number=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|sp=us}}, and an avoirdupois ounce into {{convert|300|sqft|disp=flip|sp=us}}. Gold leaf can be beaten thin enough to become semi-transparent. Light transmitted through gold 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|archive-url=http://web.archive.org/web/20150113233324/http://news.coinupdate.com/largest-private-refinery-discovers-gold-plated-tungsten-bar-0171/|archive-date=2015-01-13}}</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 }}</ref>

=== Color === {{Main|Colored gold}} thumb|upright|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 a well-known example of relativistic quantum chemistry. The 5d-6s band gap is greatly reduced when relativity is included in theoretical calculations, and this is thought to account for the yellow color, although a full comparison of the absorption spectrum between the relativistic and non-relativistic cases has not been performed as of 2004.<ref>{{Cite journal |last=Pyykkö |first=Pekka |date=2004-08-27 |title=Theoretical Chemistry of Gold |url=https://onlinelibrary.wiley.com/doi/10.1002/anie.200300624 |journal=Angewandte Chemie International Edition |language=en |volume=43 |issue=34 |pages=4412–4456 |doi=10.1002/anie.200300624 |issn=1433-7851 |quote=Finally, the attribution of the yellow color of gold to relativity rests on the result that the relativistic interband energy between the top of the 5d band and the Fermi level in the half-filled 6s band, 2.4 eV, is close to the experimental value of 2.38 eV, whereas the NR interband energy would be much larger. Comparative R/NR calculations of the reflectivity do not seem to exist. Similarly it would seem that the exact roles of the bulk electronic-band structure and that of surface plasmons have not yet been worked out.|url-access=subscription }}</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}}

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 }}</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 ->[\mathit{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 ->[\Delta] 2 AuF3</chem> <chem display=block>2 Au{} + 3 Cl2 ->[\Delta] 2 AuCl3</chem> <chem display=block>2 Au{} + 2 Br2 ->[\Delta] AuBr3{} + AuBr</chem> <chem display=block>2 Au{} + I2 ->[\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=dead |access-date=February 11, 2026 |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 ->[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 |bibcode=2006ACIE...45.3708R }}</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 |arxiv=2501.09181 |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 |arxiv=2501.09181 |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 |page=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|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. thumb|left|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 |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|sp=us}} 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 |work=Yahoo News |date=17 March 2013 |access-date=18 March 2013|archive-url=http://web.archive.org/web/20150403013000/https://news.yahoo.com/earthquakes-turn-water-gold-180356174.html|archive-date=2015-04-03}}</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 |archive-date=7 March 2020}}</ref>

== History == {{main|History of gold}} [[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) |page=146 |url=https://books.google.com/books?id=itIRAQAAMAAJ}}</ref>]]

The earliest recorded metal employed by humans appears to be gold. 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 |page=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, 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 appearance in Ancient Egypt at the 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.

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" />

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>

[[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>

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>

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>

== Production == {{Main|List of countries by gold production}}

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 }}</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, in 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 |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 |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 |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}}

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 ({{Inflation|index=US|value=317|start_year=2007|r=0|fmt=eq}}), 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 |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> {| class="wikitable sortable floatright" style="text-align:right;" |+ 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''' |} === 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>[https://news.bbc.co.uk/1/hi/world/europe/642880.stm Death of a river] . 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 }}</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 |date=1924}} {{isbn||978-0-87184-308-1}} (reprint) </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>

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>

Often the prices of various platinum group metals can be much higher than gold, although gold has been used as a standard for currencies to a greater degree than the platinum group metals. 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. A paper by the National Bureau of Economic Research found that gold may be reliable as an inflation hedge over long timescales (centuries) but not over practical timescales.<ref>{{cite report |last1=Erb |first1=Claude |last2=Harvey |first2=Campbell |title=The Golden Dilemma |date=January 2013 |doi=10.3386/w18706 |doi-access=free }}</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|History of gold#Price}} 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>

== Other applications ==

=== Jewelry === [[File:CairoEgMuseumTaaMaskMostlyPhotographed.jpg|thumb|Tutankhamun's gold funerary mask at the Egyptian Museum in Cairo, Egypt in 2016]] Pure (24k) gold is often 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, 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, though not as corrosion-proof as platinum jewelry. The Japanese craft of Mokume-gane exploits the color contrasts between laminated colored gold alloys to produce decorative wood-grain effects.

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 ({{Inflation|index=US|value=2.82|start_year=2022|r=0|fmt=eq}}) in each phone adds to US$2.82 billion in gold from just this application ({{Inflation|index=US|value=2820000000|start_year=2022|r=0|fmt=eq}}).<ref>{{Cite web |title=The Many Uses of Gold |url=http://www.usfunds.com/slideshows/the-many-uses-of-gold/ |archive-url=http://web.archive.org/web/20211024065321/https://www.usfunds.com/slideshows/the-many-uses-of-gold/ |archive-date=24 October 2021 |access-date=4 November 2014}}</ref>

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|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 is the only of these three with zero corrosion). 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>

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).

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> It can be applied as gold leaf, flake or dust for decorative purposes. Since metallic gold is generally considered inert to all body chemistry, it has no taste, provides no nutrition, and leaves the body unaltered.<ref name=KingUses>{{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> 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>

Decorative use of gold flake goes back to medieval Europe as a decoration in food and drinks among nobility.<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> Leaf or flakes are used today in sweets and drinks.<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> Vark is a foil or leaf composed of a pure metal that can include 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.

Danziger 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 (~ $1,000, {{Inflation|index=US|value=1000|start_year=2009|r=0|fmt=eq}}) cocktails which contain flakes of gold leaf.<ref name=KingUses />{{verify inline|date=March 2026}}

=== 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]]

* Gold and its salts produce 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 |work=About.com Education |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 }}</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 |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 |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 == {{Portal|Chemistry}} 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 (color), a range of colors * 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}} * Royal Society of Chemistry: [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], * US Environmental Protection Agency: {{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 }} * US Geological Service (Mineral Commodity Summaries 2025): [https://pubs.usgs.gov/periodicals/mcs2025/mcs2025.pdf#page=82 Gold] * [https://www.brooklynmuseum.org/exhibitions/solid-gold Solid Gold] 2024-25 exhibit at the Brooklyn Museum displaying the use of gold in works of art, fashion, film, music, and design

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