In 2023, theworld's largest gold producer was China, followed by Russia and Australia.[12] As of 2020[update], a total of around 201,296tonnes of gold exist above ground.[13] This is equal to a cube, with each side measuring roughly 21.7 meters (71 ft). The world's consumption of new gold produced is about 50% in jewelry, 40% ininvestments, and 10% inindustry.[14] 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-resistantelectrical connectors in all types of computerized devices (its chief industrial use). Gold is also used ininfrared shielding, the production ofcolored glass,gold leafing, andtooth restoration. Certaingold salts are still used asanti-inflammatory agents in medicine.
Characteristics
Gold can be drawn into a monatomic wire, and then stretched more before it breaks.[15]A gold nugget of 5 mm (0.20 in) in size can be hammered into agold foil of about 0.5 m2 (5.4 sq ft) in area.
Gold is the mostmalleable of all metals. It can be drawn into a wire of single-atom width, and then stretched considerably before it breaks.[15] Such nanowires distort via the formation, reorientation, and migration ofdislocations andcrystal twins without noticeable hardening.[16] A single gram of gold can be beaten into a sheet of 1 square metre (11 sq ft), and anavoirdupois ounce into 28 square metres (300 sq ft). Gold leaf can be beaten thin enough to become semi-transparent. The transmitted light appears greenish-blue because gold strongly reflects yellow and red.[17] Such semi-transparent sheets also strongly reflectinfrared light, making them useful as infrared (radiant heat) shields in the visors of heat-resistant suits and in sun visors forspacesuits.[18] Gold is a goodconductor of heat andelectricity.
Gold has a density of 19.3 g/cm3, almost identical to that oftungsten at 19.25 g/cm3; as such, tungsten has been used in thecounterfeiting ofgold bars, such as by plating a tungsten bar with gold.[19][20][21][22] By comparison, the density oflead is 11.34 g/cm3, and that of the densest element,osmium, is22.588±0.015 g/cm3.[23]
Gold bars, also called ingots or bullionDifferent colors ofAg–Au–Cu alloys
Whereas most metals are gray or silvery white, gold is slightly reddish-yellow.[24] This color is determined by the frequency ofplasma oscillations among the metal's valence electrons, in the ultraviolet range for most metals but in the visible range for gold due torelativistic effects affecting theorbitals around gold atoms.[25][26] Similar effects impart a golden hue to metalliccaesium.
Common colored gold alloys include the distinctive eighteen-karatrose gold created by the addition of copper. Alloys containingpalladium ornickel are also important in commercial jewelry as these produce white gold alloys. Fourteen-karat gold-copper alloy is nearly identical in color to certainbronze alloys, and both may be used to produce police and otherbadges. Fourteen- and eighteen-karat gold alloys with silver alone appear greenish-yellow and are referred to asgreen gold. Blue gold can be made by alloying withiron, and purple gold can be made by alloying withaluminium. Less commonly, addition ofmanganese,indium, and other elements can produce more unusual colors of gold for various applications.[27]
Colloidal gold, used by electron-microscopists, is red if the particles are small; larger particles of colloidal gold are blue.[28]
Gold has only one stableisotope,197 Au, which is also its only naturally occurring isotope, so gold is both amononuclidic andmonoisotopic element. Thirty-sixradioisotopes have been synthesized, ranging inatomic mass from 169 to 205. The most stable of these is195 Au with ahalf-life of 186.1 days. The least stable is171 Au, which decays byproton emission with a half-life of 30 μs. Most of gold's radioisotopes with atomic masses below 197 decay by some combination ofproton emission,α decay, andβ+ decay. The exceptions are195 Au, which decays by electron capture, and196 Au, which decays most often by electron capture (93%) with a minorβ− decay path (7%).[29] All of gold's radioisotopes with atomic masses above 197 decay by β− decay.[30]
At least 32nuclear isomers have also been characterized, ranging in atomic mass from 170 to 200. Within that range, only178 Au,180 Au,181 Au,182 Au, and188 Au do not have isomers. Gold's most stable isomer is198m2 Au with a half-life of 2.27 days. Gold's least stable isomer is177m2 Au with a half-life of only 7 ns.184m1 Au has three decay paths: β+ decay,isomeric transition, and alpha decay. No other isomer or isotope of gold has three decay paths.[30]
The possible production of gold from a more common element, such aslead, has long been a subject of human inquiry, and the ancient and medieval discipline ofalchemy often focused on it; however, the transmutation of the chemical elements did not become possible until the understanding ofnuclear physics in the 20th century. The first synthesis of gold was conducted by Japanese physicistHantaro Nagaoka, who synthesized gold frommercury in 1924 by neutron bombardment.[31] An American team, working without knowledge of Nagaoka's prior study, conducted the same experiment in 1941, achieving the same result and showing that theisotopes of gold produced by it were allradioactive.[32] In 1980,Glenn Seaborg transmuted several thousand atoms of bismuth into gold at the Lawrence Berkeley Laboratory.[33][34] 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.[35]
Although gold is the most noble of the noble metals,[36][37] it still forms many diverse compounds. Theoxidation 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 softligands such asthioethers,thiolates, andorganophosphines. Au(I) compounds are typically linear. A good example isAu(CN)−2, which is the soluble form of gold encountered in mining. The binarygold halides, such asAuCl, form zigzag polymeric chains, again featuring linear coordination at Au. Mostdrugs based on gold are Au(I) derivatives.[38]
Unlike sulfur, phosphorus reacts directly with gold at elevated temperatures to producegold phosphide (Au2P3).[45]
Gold readily dissolves inmercury at room temperature to form anamalgam, and formsalloys with many other metals at higher temperatures. These alloys can be produced to modify the hardness and other metallurgical properties, to controlmelting point or to create exotic colors.[27]
Gold is unaffected by most acids. It does not react withhydrofluoric,hydrochloric,hydrobromic,hydriodic,sulfuric, ornitric acid. It does react withselenic acid, and is dissolved byaqua regia, a 1:3 mixture ofnitric acid andhydrochloric 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, formingAuCl−4 ions, orchloroauric acid, thereby enabling further oxidation:
Commonoxidation states of gold include +1 (gold(I) or aurous compounds) and +3 (gold(III) or auric compounds). Gold ions in solution are readilyreduced andprecipitated as metal by adding any other metal as thereducing agent. The added metal isoxidized 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.
Gold also has a –1 oxidation state in covalent complexes with thegroup 4 transition metals, such as in titanium tetraauride and the analogous zirconium and hafnium compounds. These chemicals are expected to form gold-bridgeddimers in a manner similar totitanium(IV) hydride.[49]
Gold(II) compounds are usuallydiamagnetic with Au–Au bonds such as [Au(CH2)2P(C6H5)2]2Cl2. The evaporation of a solution ofAu(OH)3 in concentratedH2SO4 produces red crystals ofgold(II) sulfate,Au2(SO4)2. Originally thought to be a mixed-valence compound, it has been shown to containAu4+2 cations, analogous to the better-knownmercury(I) ion,Hg2+2.[50][51] A gold(II) complex, thetetraxenonogold(II) cation, which containsxenon as a ligand, occurs in[AuXe4](Sb2F11)2.[52] In September 2023, a novel type ofmetal-halide perovskite material consisting of Au3+ and Au2+ cations in its crystal structure has been found.[53] It has been shown to be unexpectedly stable at normal conditions.
Some gold compounds exhibitaurophilic 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 thanvan der Waals bonding. The interaction is estimated to be comparable in strength to that of ahydrogen bond.
Well-defined cluster compounds are numerous.[47] In some cases, gold has a fractional oxidation state. A representative example is the octahedral species{Au(P(C6H5)3)}2+6.
Origin
Gold production in the universe
Schematic of a NE (left) to SW (right) cross-section through the 2.020-billion-year-oldVredefort impact structure inSouth Africa and how it distorted the contemporary geological structures. The present erosion level is shown.Johannesburg is located where theWitwatersrand Basin (the yellow layer) is exposed at the "present surface" line, just inside the crater rim, on the left. Not to scale.
Traditionally, gold in the universe is thought to have formed by ther-process (rapid neutron capture) insupernova nucleosynthesis,[57] but more recently it has been suggested that gold and other elements heavier thaniron may also be produced in quantity by the r-process in thecollision ofneutron stars.[58] In both cases, satellite spectrometers at first only indirectly detected the resulting gold.[59] However, in August 2017, the spectroscopic signatures of heavy elements, including gold, were observed by electromagnetic observatories in theGW170817 neutron star merger event, aftergravitational wave detectors confirmed the event as a neutron star merger.[60] Current astrophysical models suggest that this single neutron star merger event generated between 3 and 13Earth masses of gold. This amount, along with estimations of the rate of occurrence of these neutron star merger events, suggests that such mergers may produce enough gold to account for most of the abundance of this element in the universe.[61]
Gold which is reachable by humans has, in one case, been associated with a particular asteroid impact. The asteroid that formedVredefort impact structure 2.020 billion years ago is often credited with seeding theWitwatersrand basin inSouth Africa with the richest gold deposits on earth.[64][65][66][67] However, this scenario is now questioned. The gold-bearingWitwatersrand rocks were laid down between 700 and 950 million years before the Vredefort impact.[68][69] These gold-bearing rocks had furthermore been covered by a thick layer of Ventersdorp lavas and theTransvaal 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 theWitwatersrand basin in such a way that the gold-bearing rocks were brought to the presenterosion surface inJohannesburg, on theWitwatersrand, just inside the rim of the original 300 km (190 mi) diameter crater caused by the meteor strike. The discovery of the deposit in 1886 launched theWitwatersrand Gold Rush. Some 22% of all the gold that is ascertained to exist today on Earth has been extracted from these Witwatersrand rocks.[69]
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, asplanetesimals formed themantle. In 2017, an international group of scientists established that gold "came to the Earth's surface from the deepest regions of our planet",[70] the mantle, as evidenced by their findings atDeseado Massif in theArgentinian Patagonia.[71][clarification needed]
On Earth, gold is found inores in rock formed from thePrecambrian time onward.[72] It most often occurs as anative metal, typically in a metalsolid solution with silver (i.e. as a gold/silveralloy). Such alloys usually have a silver content of 8–10%.Electrum is elemental gold with more than 20% silver, and is commonly known aswhite gold. Electrum's color runs from golden-silvery to silvery, dependent upon the silver content. The more silver, the lower thespecific gravity.
Gold in pyrite
Native gold occurs as very small to microscopic particles embedded in rock, often together withquartz orsulfide minerals such as "fool's gold", which is apyrite.[73] These are calledlode deposits. The metal in a native state is also found in the form of free flakes, grains or largernuggets[72] that have been eroded from rocks and end up inalluvial deposits calledplacer deposits. Such free gold is always richer at the exposed surface of gold-bearing veins, owing to theoxidation 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.
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.[74]
A 2013 study has claimed water in faults vaporizes during an earthquake, depositing gold. When an earthquake strikes, it moves along afault. Water often lubricates faults, filling in fractures and jogs. About 10 kilometres (6.2 mi) 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.[75]
Seawater
The world'soceans contain gold. Measured concentrations of gold in the Atlantic and Northeast Pacific are 50–150femtomol/L or 10–30 parts perquadrillion (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'soceans would hold 15,000 tonnes of gold.[76] 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 fromsea water, but they were either mistaken or acted in an intentional deception.Prescott Jernegan ran a gold-from-seawater swindle in theUnited States in the 1890s, as did an English fraudster in the early 1900s.[77]Fritz Haber did research on the extraction of gold from sea water in an effort to help payGermany's reparations followingWorld War I.[78] 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.[79]
History
Oldest golden artifacts in the world (4600–4200 BC) from Varna necropolis, Bulgaria — grave offerings on exposition inVarna Museum.An Indian tribute-bearer atApadana, from theAchaemenidsatrapy ofHindush, carrying gold on a yoke, circa 500 BC.[80]TheMuisca raft, between circa 600–1600 AD. The figure refers to the ceremony of the legend ofEl Dorado. Thezipa used to cover his body in gold dust, and from hisraft, he offered treasures to theGuatavita goddess in the middle of thesacred lake. This old Muisca tradition became the origin of the legend of El Dorado. This Muisca raft figure is on display in theGold Museum, Bogotá, Colombia.
The earliest recorded metal employed by humans appears to be gold, which can be foundfree or "native". Small amounts of natural gold have been found in Spanish caves used during the latePaleolithic period,c. 40,000 BC.[81]
The oldest gold artifacts in the world are fromBulgaria and are dating back to the 5th millennium BC (4,600 BC to 4,200 BC), such as those found in theVarna Necropolis near Lake Varna and theBlack Sea coast, thought to be the earliest "well-dated" finding of gold artifacts in history.[82][72][83]
Gold artifacts probably made their first appearance in Ancient Egypt at the very beginning of the pre-dynastic period, at the end of the fifth millennium BC and the start of the fourth, and smelting was developed during the course of the 4th millennium; gold artifacts appear in the archeology of Lower Mesopotamia during the early 4th millennium.[84] As of 1990, gold artifacts found at theWadi Qana cave cemetery of the4th millennium BC inWest Bank were the earliest from the Levant.[85] Gold artifacts such as thegolden hats and theNebra disk appeared in Central Europe from the 2nd millennium BCBronze Age.
The oldest known map of a gold mine was drawn in the 19th Dynasty of Ancient Egypt (1320–1200 BC), whereas the first written reference to gold was recorded in the 12th Dynasty around 1900 BC.[86]Egyptian hieroglyphs from as early as 2600 BC describe gold, which KingTushratta of theMitanni claimed was "more plentiful than dirt" in Egypt.[87] Egypt and especiallyNubia had the resources to make them major gold-producing areas for much of history. One of the earliest known maps, known as theTurin Papyrus Map, shows the plan of agold mine in Nubia together with indications of the localgeology. The primitive working methods are described by bothStrabo andDiodorus Siculus, and includedfire-setting. Large mines were also present across theRed Sea in what is nowSaudi Arabia.
Gold is mentioned frequently in theOld Testament, starting withGenesis 2:11 (atHavilah), the story of thegolden calf, and many parts of the temple including theMenorah and the golden altar. In theNew Testament, it is included with the gifts of themagi in the first chapters of Matthew. TheBook of Revelation 21:21 describes the city ofNew Jerusalem as having streets "made of pure gold, clear as crystal". Exploitation of gold in the south-east corner of theBlack Sea is said to date from the time ofMidas, and this gold was important in the establishment of what is probably the world's earliest coinage inLydia around 610 BC.[92] The legend of thegolden fleece dating from eighth century BCE may refer to the use of fleeces to trap gold dust fromplacer deposits in the ancient world. From the 6th or 5th century BC, theChu (state) circulated theYing Yuan, one kind of square gold coin.
InRoman metallurgy, new methods for extracting gold on a large scale were developed by introducinghydraulic mining methods, especially inHispania from 25 BC onwards and inDacia from 106 AD onwards. One of their largest mines was atLas Medulas inLeón, where seven longaqueducts enabled them to sluice most of a large alluvial deposit. The mines atRoşia Montană inTransylvania were also very large, and until very recently,[when?] still mined by opencast methods. They also exploited smaller deposits inBritain, such as placer and hard-rock deposits atDolaucothi. The various methods they used are well described byPliny the Elder in hisencyclopediaNaturalis Historia written towards the end of the first century AD.
DuringMansa Musa's (ruler of theMali Empire from 1312 to 1337)hajj toMecca in 1324, he passed throughCairo in July 1324, and was reportedly accompanied by acamel 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 highinflation.[93] A contemporary Arab historian remarked:
Gold was at a high price in Egypt until they came in that year. The mithqal did not go below 25 dirhams and was generally above, but from that time its value fell and it cheapened in price and has remained cheap till now. The mithqal does not exceed 22 dirhams or less. This has been the state of affairs for about twelve years until this day by reason of the large amount of gold which they brought into Egypt and spent there [...].
Gold coin ofEucratides I (171–145 BC), one of the Hellenistic rulers of ancientAi-Khanoum. This is the largest known gold coin minted in antiquity (169.2 g (5.97 oz); 58 mm (2.3 in)).[95]
The European exploration of the Americas was fueled in no small part by reports of the gold ornaments displayed in great profusion byNative American peoples, especially inMesoamerica,Peru,Ecuador andColombia. TheAztecs regarded gold as the product of the gods, calling it literally "god excrement" (teocuitlatl inNahuatl), and afterMoctezuma II was killed, most of this gold was shipped to Spain.[96] However, for theindigenous peoples of North America gold was considered useless and they saw much greater value in otherminerals which were directly related to their utility, such asobsidian,flint, andslate.[97]
El Dorado is applied to a legendary story in which precious stones were found in fabulous abundance along with gold coins. The concept of El Dorado underwent several transformations, and eventually accounts of the previous myth were also combined with those of a legendary lost city. El Dorado, was the term used by the Spanish Empire to describe a mythical tribal chief (zipa) of the Muisca native people inColombia, who, as an initiation rite, covered himself with gold dust and submerged inLake Guatavita. The legends surrounding El Dorado changed over time, as it went from being a man, to a city, to a kingdom, and then finally to an empire.[citation needed]
Beginning in theearly modern period, Europeanexploration andcolonization ofWest 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".[98] From the late 15th to early 19th centuries, European trade in the region was primarily focused in gold, along withivory andslaves.[99] The gold trade in West Africa was dominated by theAshanti Empire, who initially traded with thePortuguese before branching out and trading withBritish,French,Spanish andDanish merchants.[100] British desires to secure control of West African gold deposits played a role in theAnglo-Ashanti wars of the late 19th century, which saw the Ashanti Empireannexed by Britain.[101]
Gold played a role in western culture, as a cause for desire and of corruption, as told in children'sfables such asRumpelstiltskin—where Rumpelstiltskin turns hay into gold for the peasant's daughter in return for her child when she becomes a princess—and the stealing of the hen that lays golden eggs inJack and the Beanstalk.
75% of the presently accounted for gold has been extracted since 1910, two-thirds since 1950.[citation needed]
One main goal of thealchemists was to produce gold from other substances, such aslead — presumably by the interaction with a mythical substance called thephilosopher'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'schemistry, which can produce gold (albeit uneconomically) by usingnuclear transmutation.[102] Their symbol for gold was the circle with a point at its center (☉), which was also theastrological symbol and the ancientChinese character for theSun.
TheDome of the Rock is covered with an ultra-thin golden glassier. TheSikh Golden temple, theHarmandir Sahib, is a building covered with gold. Similarly theWat Phra Kaew emeraldBuddhisttemple (wat) inThailand has ornamental gold-leafed statues and roofs. Some European king and queen'scrowns were made of gold, and gold was used for thebridal crown since antiquity. An ancient Talmudic text circa 100 AD describesRachel, wife of Rabbi Akiva, receiving a "Jerusalem of Gold" (diadem). A Greek burial crown made of gold was found in a grave circa 370 BC.
Neoclassical washstand (athénienne or lavabo), 1800–1814, legs, base and shelf of yew wood, gilt bronze mounts, iron plate beneath shelf, Metropolitan Museum of Art
The symbolAu is from theLatinaurum'gold'.[112] The Proto-Indo-European ancestor ofaurum was*h₂é-h₂us-o-, meaning'glow'. This word is derived from the sameroot (Proto-Indo-European*h₂u̯es-'to dawn') as*h₂éu̯sōs, the ancestor of the Latin wordaurora'dawn'.[113] This etymological relationship is presumably behind the frequent claim in scientific publications thataurum meant'shining dawn'.[114]
In popular culture gold is a high standard of excellence, often used in awards.[48] Great achievements are frequently rewarded with gold, in the form ofgold medals, goldtrophies and other decorations. Winners of athletic events and other graded competitions are usually awarded a gold medal. Many awards such as theNobel Prize are made from gold as well. Other award statues and prizes are depicted in gold or aregold plated (such as theAcademy Awards, theGolden Globe Awards, theEmmy Awards, thePalme d'Or, and theBritish Academy Film Awards).[115]
Aristotle in hisethics used gold symbolism when referring to what is now known as thegolden mean. Similarly, gold is associated with perfect or divine principles, such as in the case of thegolden ratio and theGolden Rule. Gold is further associated with the wisdom of aging and fruition. The fiftiethwedding anniversary is golden. A person's most valued or most successful latter years are sometimes considered "golden years" or "golden jubilee". The height of a civilization is referred to as agolden age.[116]
InIslam,[119] gold (along withsilk)[120][121] is often cited as being forbidden for men to wear.[122]Abu Bakr al-Jazaeri, quoting ahadith, said that "[t]he wearing of silk and gold are forbidden on the males of my nation, and they are lawful to their women".[123] This, however, has not been enforced consistently throughout history, e.g. in the Ottoman Empire.[124] Further, small gold accents on clothing, such as inembroidery, may be permitted.[125]
According toChristopher Columbus, those who had something of gold were in possession of something of great value on Earth and a substance to even help souls to paradise.[127]
Wedding rings are typically made of gold. It is long lasting and unaffected by the passage of time and may aid in the ring symbolism of eternal vows before God and the perfection the marriage signifies. InOrthodox Christian wedding ceremonies, the wedded couple is adorned with a golden crown (though some opt for wreaths, instead) during the ceremony, an amalgamation of symbolic rites.[further explanation needed]
On 24 August 2020,Israeli archaeologists discovered a trove of earlyIslamic gold coins near the central city ofYavne. Analysis of the extremely rare collection of 425 gold coins indicated that they were from the late 9th century. Dating to around 1,100 years back, the gold coins were from theAbbasid Caliphate.[128]
According to theUnited States Geological Survey in 2016, about 5,726,000,000 troy ounces (178,100 t) of gold has been accounted for, of which 85% remains in active use.[129]
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 fromSouth Africa. Production in 1970 accounted for 79% of the world supply, about 1,480 tonnes. In 2007China (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.[130]
In 2023,China was the world's leading gold-mining country, followed in order by Russia, Australia, Canada, the United States and Ghana.[12]
Relative sizes of an 860 kg (1,900 lb) block of gold ore and the 30 g (0.96 ozt) of gold that can be extracted from it,Toi gold mine,Japan.
In South America, the controversial projectPascua Lama aims at exploitation of rich fields in the high mountains ofAtacama Desert, at the border betweenChile andArgentina.
It has been estimated that up to one-quarter of the yearly global gold production originates from artisanal or small scale mining.[131][132][133]
The city ofJohannesburg located in South Africa was founded as a result of theWitwatersrand 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 theWitwatersrand basin, which is a 5–7 km (3.1–4.3 mi) thick layer ofarchean rocks located, in most places, deep under theFree State,Gauteng and surrounding provinces.[134] These Witwatersrand rocks are exposed at the surface on theWitwatersrand, 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 theVredefort Dome which lies close to the center of the Witwatersrand basin.[68][134] From these surface exposures the basindips extensively, requiring some of the mining to occur at depths of nearly 4,000 m (13,000 ft), making them, especially theSavuka andTauTona mines to the south-west of Johannesburg, the deepest mines on Earth. The gold is found only in six areas wherearchean rivers from the north and north-west formed extensive pebblyBraided river deltas before draining into the "Witwatersrand sea" where the rest of the Witwatersrand sediments were deposited.[134]
TheSecond Boer War of 1899–1901 between theBritish Empire and theAfrikanerBoers was at least partly over the rights of miners and possession of the gold wealth in South Africa.
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 theReed Gold Mine near Georgeville, North Carolina in 1803.[135] The first major gold strike in the United States occurred in a small north Georgia town calledDahlonega.[136] Further gold rushes occurred inCalifornia,Colorado, theBlack Hills,Otago in New Zealand, a number of locations acrossAustralia,Witwatersrand in South Africa, and theKlondike in Canada.
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 inopen-pit mines are 1–5 ppm; ore grades in underground orhard rock mines are usually at least 3 ppm. Because ore grades of 30 ppm are usually needed before gold is visible to the naked eye, in most gold mines the gold is invisible.
The average gold mining and extraction costs were about $317 per troy ounce in 2007, but these can vary widely depending on mining type and ore quality; global mine production amounted to 2,471.1 tonnes.[138]
After initial production, gold is often subsequently refined industrially by theWohlwill process which is based onelectrolysis or by theMiller 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.[139][140] Other methods of assaying and purifying smaller amounts of gold include parting and inquartation as well ascupellation, or refining methods based on the dissolution of gold in aqua regia.[141]
Recycling
In 1997, recycled gold accounted for approximately 20% of the 2700 tons of gold supplied to the market.[142] Jewelry companies such as Generation Collection and computer companies includingDell conduct recycling.[143]
As of 2020, the amount ofcarbon dioxideCO2 produced in mining a kilogram of gold is 16 tonnes, while recycling a kilogram of gold produces 53 kilograms ofCO2 equivalent. Approximately 30 percent of the global gold supply is recycled and not mined as of 2020.[144]
Consumption
This article needs to beupdated. Please help update this article to reflect recent events or newly available information.(May 2022)
Gold jewelry consumption by country (in tonnes)[145][146][147]
Gold production is associated with contribution to hazardouspollution.[150]
Low-grade gold ore may contain less than oneppm gold metal; such ore isground and mixed withsodium cyanide to dissolve the gold. Cyanide is a highly poisonous chemical, which can kill living creatures when exposed in minute quantities. Manycyanide spills[151] 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.[152][153] Up to thirty tons of used ore can be dumped as waste for producing one troy ounce of gold.[154] 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 intosulfuric acid which in turn dissolves these heavy metals facilitating their passage into surface water and ground water. This process is calledacid mine drainage. These gold ore dumps contain long-term, highlyhazardous waste.[154]
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.[155] 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 ofmethylmercury.Mercury poisoning in humans can cause severe brain damage.[156]
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 25kWh of electricity per gram of gold produced.[157]
The first known coins containing gold were struck in Lydia, Asia Minor, around 600 BC.[92] Thetalent 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.[159] From an earlier preference in using silver, European economies re-established the minting of gold as coinage during the thirteenth and fourteenth centuries.[160]
Bills (that mature into gold coin) andgold certificates (convertible into gold coin at the issuing bank) added to the circulating stock ofgold standard money in most 19th century industrial economies. In preparation forWorld 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.
AfterWorld War II gold was replaced by a system of nominallyconvertible currencies related by fixed exchange rates following theBretton 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.[161]
Central banks continue to keep a portion of their liquid reserves as gold in some form, and metals exchanges such as theLondon Bullion Market Association still clear transactions denominated in gold, including future delivery contracts. Today,gold mining output is declining.[162] With the sharp growth of economies in the 20th century, and increasing foreign exchange, the world'sgold 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 goldfuture 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 bykarat (k). Pure gold (commercially termedfine 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 calledcrown gold,[163] for hardness (American gold coins for circulation after 1837 contain an alloy of 0.900 fine gold, or 21.6 kt).[164]
Although the prices of someplatinum group metals can be much higher, gold has long been considered the most desirable ofprecious metals, and its value has been used as the standard for manycurrencies. 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 byThomas More in his treatiseUtopia. 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.
TheISO 4217 currency code of gold is XAU.[165] Many holders of gold store it in form ofbullion coins orbars as a hedge againstinflation or other economic disruptions, though its efficacy as such has been questioned; historically, it has not proven itself reliable as a hedging instrument.[166] Modernbullion coins for investment or collector purposes do not require good mechanical wear properties; they are typically fine gold at 24k, although theAmerican Gold Eagle and the Britishgold sovereign continue to be minted in 22k (0.92) metal in historical tradition, and the South AfricanKrugerrand, first released in 1967, is also 22k (0.92).[167]
Like other precious metals, gold is measured bytroy weight and by grams. The proportion of gold in the alloy is measured bykarat (k), with 24 karat (24k) being pure gold (100%), and lower karat numbers proportionally less (18k = 75%). The purity of agold bar or coin can also be expressed as a decimal figure ranging from 0 to 1, known as themillesimal fineness, such as 0.995 being nearly pure.
The price of gold is determined through trading in the gold andderivatives markets, but a procedure known as theGold Fixing inLondon, 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.[169] As of February 2025[update], gold was valued at around $92 per gram ($2,850 per troy ounce).
History
Historically goldcoinage was widely used as currency; whenpaper money was introduced, it typically was areceipt redeemable for gold coin orbullion. In amonetary system known as thegold standard, a certainweight of gold was given the name of a unit of currency. For a long period, the United States government set the value of the US dollar so that onetroy ounce was equal to $20.67 ($0.665 per gram), but in 1934 the dollar was devalued to $35.00 per troy ounce ($0.889/g). By 1961, it was becoming hard to maintain this price, anda pool of US and European banks agreed to manipulate the market to prevent furthercurrency devaluation against increased gold demand.[170]
The largest gold depository in the world is that of theU.S. Federal Reserve Bank inNew York, which holds about 3%[171] of the gold known to exist and accounted for today, as does the similarly ladenU.S. Bullion Depository atFort Knox. In 2005 theWorld Gold Council estimated total global gold supply to be 3,859 tonnes and demand to be 3,754 tonnes, giving a surplus of 105 tonnes.[172]
After 15 August 1971Nixon shock, the price began to greatly increase,[173] and between 1968 and 2000 the price of gold ranged widely, from a high of $850 per troy ounce ($27.33/g) on 21 January 1980, to a low of $252.90 per troy ounce ($8.13/g) on 21 June 1999 (London Gold Fixing).[174] Prices increased rapidly from 2001, but the 1980 high was not exceeded until 3 January 2008, when a new maximum of $865.35 pertroy ounce was set.[175] Another record price was set on 17 March 2008, at $1023.50 per troy ounce ($32.91/g).[175]
On 2 December 2009, gold reached a new high closing at $1,217.23.[176] Gold further rallied hitting new highs in May 2010 after the European Union debt crisis prompted further purchase of gold as a safe asset.[177][178] On 1 March 2011, gold hit a new all-time high of $1432.57, based oninvestor concerns regarding ongoingunrest inNorth Africa as well as in theMiddle East.[179]
From April 2001 to August 2011, spot gold prices more than quintupled in value against the US dollar, hitting a new all-time high of $1,913.50 on 23 August 2011,[180] prompting speculation that the longsecular bear market had ended and abull market had returned.[181] However, the price then began a slow decline towards $1200 per troy ounce in late 2014 and 2015.
In August 2020, the gold price picked up to US$2060 per ounce after a total growth of 59% from August 2018 to October 2020, a period during which it outplaced the Nasdaq total return of 54%.[182]
Gold futures are traded on the COMEX exchange.[183] These contacts are priced in USD per troy ounce (1 troy ounce = 31.1034768 grams).[184] Below are theCQG contract specifications outlining the futures contracts:
Because of the softness of pure (24k) gold, it is usuallyalloyed with other metals for use in jewelry, altering its hardness and ductility, melting point, color and other properties. Alloys with lowerkarat rating, typically 22k, 18k, 14k or 10k, contain higher percentages of copper, silver, palladium or other base metals in the alloy.[27] Nickel is toxic, and its release from nickel white gold is controlled by legislation in Europe.[27] Palladium-gold alloys are more expensive than those using nickel.[185] High-karat white gold alloys are more resistant to corrosion than are either pure silver orsterling silver. The Japanese craft ofMokume-gane exploits the color contrasts between laminated colored gold alloys to produce decorative wood-grain effects.
By 2014, the gold jewelry industry was escalating despite a dip in gold prices. Demand in the first quarter of 2014 pushed turnover to $23.7 billion according to aWorld Gold Council report.
Goldsolder is used for joining the components of gold jewelry by high-temperature hard soldering orbrazing. If the work is to be ofhallmarking 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 intothread and used inembroidery.
Electronics
Only 10% of the world consumption of new gold produced goes to industry,[14] but by far the most important industrial use for new gold is in fabrication of corrosion-freeelectrical connectors in computers and other electrical devices. For example, according to the World Gold Council, a typical cell phone may contain 50 mg of gold, worth about three dollars. But since nearly one billion cell phones are produced each year, a gold value of US$2.82 in each phone adds to US$2.82 billion in gold from just this application.[186] (Prices updated to November 2022)
Though gold is attacked by free chlorine, its good conductivity and general resistance to oxidation and corrosion in other environments (including resistance to non-chlorinated acids) has led to its widespread industrial use in the electronic era as a thin-layer coating onelectrical connectors, thereby ensuring good connection. For example, gold is used in the connectors of the more expensive electronics cables, such as audio, video andUSB cables. The benefit of using gold over other connector metals such astin 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 (certaincomputers, communications equipment,spacecraft,jet aircraft engines) remains very common.[187]
The concentration of free electrons in gold metal is 5.91×1022 cm−3.[189] Gold is highlyconductive to electricity and has been used forelectrical wiring in some high-energy applications (only silver and copper are more conductive per volume, but gold has the advantage of corrosion resistance). For example, gold electrical wires were used during some of theManhattan Project's atomic experiments, but large high-current silver wires were used in thecalutron 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.[190]
Medicine
There are only two gold compounds currently employed as pharmaceuticals in modern medicine (sodium aurothiomalate andauranofin), used in the treatment of arthritis and other similar conditions in the US due to theiranti-inflammatory properties. These drugs have been explored as a means to help to reduce the pain and swelling ofrheumatoid arthritis, and also (historically) againsttuberculosis and some parasites.[191][192]
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)[192] and known toDioscorides.[193][194] 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.
The apparent paradox[further explanation needed] of the actual toxicology of the substance suggests the possibility of serious gaps in the understanding of the action of gold in physiology.[196] 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).
Colloidal gold varies in color with the size of gold particles
Gold alloys are used inrestorative dentistry, especially in tooth restorations, such ascrowns and permanentbridges. 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 ofgold 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 withcitrate orascorbate ions. Colloidal gold is used in research applications in medicine, biology andmaterials science. The technique ofimmunogold 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.[197] In ultrathin sections of tissues viewed byelectron microscopy, the immunogold labels appear as extremely dense round spots at the position of theantigen.[198]
Gold, or alloys of gold andpalladium, are applied as conductive coating to biological specimens and other non-conducting materials such as plastics and glass to be viewed in ascanning electron microscope. The coating, which is usually applied bysputtering with anargonplasma, has a triple role in this application. Gold's very high electrical conductivity drainselectrical charge to earth, and its very high density provides stopping power for electrons in theelectron 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 thespatial resolution of the image. Gold also produces a high output ofsecondary 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.[199]
Gold can be used in food and has theE number 175.[202] In 2016, theEuropean 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 goldnanoparticles in the food additive, and that gold nanoparticles have been shown to begenotoxic in mammalian cellsin vitro.[203]
Gold leaf, flake or dust is used on and in some gourmet foods, notably sweets and drinks as decorative ingredient.[204] Gold flake was used by the nobility inmedieval Europe as a decoration in food and drinks,[205]
Danziger Goldwasser (German: Gold water of Danzig) orGoldwasser (English:Goldwater) is a traditional German herballiqueur[206] produced in what is todayGdańsk,Poland, andSchwabach, Germany, and contains flakes of gold leaf. There are also some expensive (c. $1000) cocktails which contain flakes of gold leaf. However, since metallic gold is inert to all body chemistry, it has no taste, it provides no nutrition, and it leaves the body unaltered.[207]
Vark is afoil composed of a pure metal that is sometimes gold,[208] and is used forgarnishing sweets in South Asian cuisine.
Gold produces a deep, intense red color when used as a coloring agent incranberry glass.
In photography, gold toners are used to shift the color ofsilver bromide black-and-white prints towards brown or blue tones, or to increase their stability. Used onsepia-toned prints, gold toners produce red tones. Kodak published formulas for several types of gold toners, which use gold as the chloride.[209]
Gold is used as the reflective layer on somehigh-end CDs.
Automobiles may use gold for heat shielding.McLaren uses gold foil in the engine compartment of itsF1 model.[210]
Gold can be manufactured so thin that it appears semi-transparent. It is used in some aircraft cockpit windows forde-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.[211]
Gold is attacked by and dissolves in alkaline solutions of potassium or sodiumcyanide, to form the salt gold cyanide—a technique that has been used in extracting metallic gold from ores in thecyanide process. Gold cyanide is theelectrolyte used in commercialelectroplating of gold onto base metals andelectroforming.
Gold chloride (chloroauric acid) solutions are used to make colloidal gold by reduction withcitrate orascorbateions. Gold chloride and gold oxide are used to make cranberry or red-colored glass, which, likecolloidal gold suspensions, contains evenly sized sphericalgold nanoparticles.[212]
Gold, when dispersed in nanoparticles, can act as aheterogeneous catalyst of chemical reactions.
In recent years, gold has been used as a symbol of pride by theautism rights movement, as its symbol Au could be seen as similar to the word "autism".[213]
Toxicity
Pure metallic (elemental) gold is non-toxic and non-irritating when ingested[214] and is sometimes used as a food decoration in the form ofgold leaf.[215] Metallic gold is also a component of the alcoholic drinksGoldschläger,Gold Strike, andGoldwasser. Metallic gold is approved as afood additive in the EU (E175 in theCodex 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.
Gold metal was votedAllergen of the Year in 2001 by the American Contact Dermatitis Society; gold contact allergies affect mostly women.[218] Despite this, gold is a relatively non-potent contact allergen, in comparison with metals likenickel.[219]
A sample of the fungusAspergillus 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.[220]
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![Minoan cup, part of the Aegina Treasure, 1850–1550 BC, gold, British Museum[103]](/mt/?noimg=&dark=on&url=https%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aAegina_treasure_10.jpg)
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![Ancient Chinese cast openwork dagger hilt, 6th–5th centuries BC, gold, British Museum[104]](/mt/?noimg=&dark=on&url=https%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aOpenwork_dagger_handle-IMG_4418-black.jpg)
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![Anglo-Saxon belt buckle from Sutton Hoo with a niello interlace pattern, 7th century, gold, British Museum[105]](/mt/?noimg=&dark=on&url=https%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aBritish_Museum_-_Room_41_(20626313758).jpg)
![Inca hollow model of a llama, 14th-15th centuries, gold, British Museum[106]](/mt/?noimg=&dark=on&url=https%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aAHOTWgold_lama.JPG)
![Renaissance hat badge that shows the Judgment of Paris, 16th century, enamelled gold, British Museum[107]](/mt/?noimg=&dark=on&url=https%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aThe_Judgement_of_Paris%2c_Waddeson_Bequest.jpg)
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![Rococo snuff box with Minerva, by Jean-Malquis Lequin, 1750–1752, gold and painted enamel, Louvre[108]](/mt/?noimg=&dark=on&url=https%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aTabati%25C3%25A8re_Minerve%2c_Mercure%2c_P%25C3%25A9gase_(Louvre%2c_OA_2121).jpg)
![Louis XVI style snuff box, by Jean Frémin, 1763–1764, gold and painted enamel, Louvre[109]](/mt/?noimg=&dark=on&url=https%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aTabati%25C3%25A8re_J-Fr%25C3%25A9min_(Louvre%2c_OA_6857).jpg)
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