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Gold

Gold is a chemical element with the symbol Au (from Latin: aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile metal in a pure form. Chemically, gold is a transition metal and a group 11 element. It is one of the least reactive chemical elements and is solid under standard conditions. Gold often occurs in free elemental (native state), as nuggets or grains, in rocks, veins, and alluvial deposits. It occurs in a solid solution series with the native element silver (as electrum), naturally alloyed with other metals like copper and palladium, and mineral inclusions such as within pyrite. Less commonly, it occurs in minerals as gold compounds, often with tellurium (gold tellurides).

Gold, 79Au
Gold
Appearancemetallic yellow
Standard atomic weight Ar°(Au)
  • 196.966570±0.000004
  • 196.97±0.01 (abridged)[1]
Gold in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Ag

Au

Rg
platinumgoldmercury
Atomic number (Z)79
Groupgroup 11
Periodperiod 6
Block  d-block
Electron configuration[Xe] 4f14 5d10 6s1
Electrons per shell2, 8, 18, 32, 18, 1
Physical properties
Phase at STPsolid
Melting point1337.33 K ​(1064.18 °C, ​1947.52 °F)
Boiling point3243 K ​(2970 °C, ​5378 °F)
Density (near r.t.)19.3 g/cm3
when liquid (at m.p.)17.31 g/cm3
Heat of fusion12.55 kJ/mol
Heat of vaporization342 kJ/mol
Molar heat capacity25.418 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 1646 1814 2021 2281 2620 3078
Atomic properties
Oxidation states−3, −2, −1, 0,[2] +1, +2, +3, +5 (an amphoteric oxide)
ElectronegativityPauling scale: 2.54
Ionization energies
  • 1st: 890.1 kJ/mol
  • 2nd: 1980 kJ/mol
Atomic radiusempirical: 144 pm
Covalent radius136±6 pm
Van der Waals radius166 pm
Spectral lines of gold
Other properties
Natural occurrenceprimordial
Crystal structureface-centered cubic (fcc)
Speed of sound thin rod2030 m/s (at r.t.)
Thermal expansion14.2 µm/(m⋅K) (at 25 °C)
Thermal conductivity318 W/(m⋅K)
Electrical resistivity22.14 nΩ⋅m (at 20 °C)
Magnetic orderingdiamagnetic[3]
Molar magnetic susceptibility−28.0×10−6 cm3/mol (at 296 K)[4]
Tensile strength120 MPa
Young's modulus79 GPa
Shear modulus27 GPa
Bulk modulus180 GPa[5]
Poisson ratio0.4
Mohs hardness2.5
Vickers hardness188–216 MPa
Brinell hardness188–245 MPa
CAS Number7440-57-5
History
Namingfrom Latin aurum, meaning gold
DiscoveryIn the Middle East (before 6000 BCE)
Symbol"Au": from Latin aurum
Main isotopes of gold
Iso­tope Decay
abun­dance half-life (t1/2) mode pro­duct
195Au syn 186.01 d ε 195Pt
196Au syn 6.165 d β+ 196Pt
β 196Hg
197Au 100% stable
198Au syn 2.69464 d β 198Hg
199Au syn 3.139 d β 199Hg
 Category: Gold
| references

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,[6][7] gold is a precious metal that has been used for coinage, jewelry, and other arts throughout recorded history. In the past, a gold standard was often implemented as a monetary policy. Gold coins ceased to be minted as a circulating currency in the 1930s, and the world gold standard was abandoned for a fiat currency system after the Nixon shock measures of 1971.

In 2020, the world's largest gold producer was China, followed by Russia and Australia.[8] A total of around 201,296 tonnes of gold exists above ground, as of 2020.[9] This is equal to a cube with each side measuring roughly 21.7 meters (71 ft). The world consumption of new gold produced is about 50% in jewelry, 40% in investments and 10% in industry.[10] Gold's high malleability, ductility, resistance to corrosion and most other chemical reactions, and 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, production of colored glass, gold leafing, and tooth restoration. Certain gold salts are still used as anti-inflammatories in medicine.

Characteristics

 
Gold can be drawn into a monatomic wire, and then stretched more before it breaks.[11]
 
A gold nugget of 5 mm (0.20 in) in size can be hammered into a gold foil of about 0.5 m2 (5.4 sq ft) in area.

Gold is the most malleable of all metals. It can be drawn into a wire of single-atom width, and then stretched considerably before it breaks.[11] Such nanowires distort via formation, reorientation and migration of dislocations and crystal twins without noticeable hardening.[12] A single gram of gold can be beaten into a sheet of 1 square metre (11 sq ft), and an avoirdupois ounce into 300 square feet (28 m2). Gold leaf can be beaten thin enough to become semi-transparent. The transmitted light appears greenish-blue, because gold strongly reflects yellow and red.[13] Such semi-transparent sheets also strongly reflect infrared light, making them useful as infrared (radiant heat) shields in visors of heat-resistant suits, and in sun-visors for spacesuits.[14] 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 counterfeiting of gold bars, such as by plating a tungsten bar with gold,[15][16][17][18] or taking an existing gold bar, drilling holes, and replacing the removed gold with tungsten rods.[19] By comparison, the density of lead is 11.34 g/cm3, and that of the densest element, osmium, is 22.588±0.015 g/cm3.[20]

Color

 
Different colors of Ag–Au–Cu alloys

Whereas most metals are gray or silvery white, gold is slightly reddish-yellow.[21] This color is determined by the frequency of plasma oscillations among the metal's valence electrons, in the ultraviolet range for most metals but in the visible range for gold due to relativistic effects affecting the orbitals around gold atoms.[22][23] 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.[24]

Colloidal gold, used by electron-microscopists, is red if the particles are small; larger particles of colloidal gold are blue.[25]

Isotopes

Gold has only one stable isotope, 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 195
Au
with a half-life of 186.1 days. The least stable is 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 195
Au
, which decays by electron capture, and 196
Au
, which decays most often by electron capture (93%) with a minor β decay path (7%).[26] All of gold's radioisotopes with atomic masses above 197 decay by β decay.[27]

At least 32 nuclear isomers have also been characterized, ranging in atomic mass from 170 to 200. Within that range, only 178
Au
, 180
Au
, 181
Au
, 182
Au
, and 188
Au
do not have isomers. Gold's most stable isomer is 198m2
Au
with a half-life of 2.27 days. Gold's least stable isomer is 177m2
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.[27]

Synthesis

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.[28] 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.[29] In 1980, Glenn Seaborg transmuted several thousand atoms of bismuth into gold at the Lawrence Berkeley Laboratory.[30][31] 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.[32]

Chemistry

 
Gold(III) chloride solution in water

Although gold is the most noble of the noble metals,[33][34] 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 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.[35]

Au(III) (referred to as the auric) is a common oxidation state, and is illustrated by gold(III) chloride, 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[36] and, up to 100 °C, is resistant to attack from ozone.[37]

 
 

Some free halogens react with gold.[38] Gold is strongly attacked by fluorine at dull-red heat[39] to form gold(III) fluoride AuF3. Powdered gold reacts with chlorine at 180 °C to form gold(III) chloride AuCl3.[40] Gold reacts with bromine at 140 °C to form gold(III) bromide AuBr3, but reacts only very slowly with iodine to form gold(I) iodide AuI.

 
 
 
 

Gold does not react with sulfur directly,[41] but gold(III) sulfide can be made by passing hydrogen sulfide through a dilute solution of gold(III) chloride or chlorauric acid.

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.[24]

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 AuCl4 ions, or chloroauric acid, thereby enabling further oxidation.

 
 

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.[41]

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 Au anion. Caesium auride (CsAu), for example, crystallizes in the caesium chloride motif;[42] rubidium, potassium, and tetramethylammonium aurides are also known.[43] Gold has the highest electron affinity of any metal, at 222.8 kJ/mol, making Au a stable species,[44] 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.[45]

Gold(II) compounds are usually diamagnetic with Au–Au bonds such as [Au(CH2)2P(C6H5)2]2Cl2. The evaporation of a solution of Au(OH)3 in concentrated H2SO4 produces red crystals of gold(II) sulfate, Au2(SO4)2. Originally thought to be a mixed-valence compound, it has been shown to contain Au4+2 cations, analogous to the better-known mercury(I) ion, Hg2+2.[46][47] A gold(II) complex, the tetraxenonogold(II) cation, which contains xenon as a ligand, occurs in [AuXe4](Sb2F11)2.[48]

Gold pentafluoride, along with its derivative anion, AuF6, and its difluorine complex, gold heptafluoride, is the sole example of gold(V), the highest verified oxidation state.[49]

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.[43] 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-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 is thought to have been produced in supernova nucleosynthesis, and from the collision of neutron stars,[50] and to have been present in the dust from which the Solar System formed.[51]

Traditionally, gold in the universe is thought to have formed by the r-process (rapid neutron capture) in supernova nucleosynthesis,[52] but more recently it has been suggested that gold and other elements heavier than iron may also be produced in quantity by the r-process in the collision of neutron stars.[53] In both cases, satellite spectrometers at first only indirectly detected the resulting gold.[54] However, in August 2017, the spectroscopic signatures of heavy elements, including gold, were observed by electromagnetic observatories in the GW170817 neutron star merger event, after gravitational wave detectors confirmed the event as a neutron star merger.[55] Current astrophysical models suggest that this single neutron star merger event generated between 3 and 13 Earth 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.[56]

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, most of the gold that is in the Earth's crust and mantle has in one model thought to have been delivered to Earth later, by asteroid impacts during the Late Heavy Bombardment, about 4 billion years ago.[57][58]

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.[59][60][61][62] However, this scenario is now questioned. The gold-bearing Witwatersrand rocks were laid down between 700 and 950 million years before the Vredefort impact.[63][64] 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 300 km (190 mi) 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.[64]

Mantle return theories

Notwithstanding the impact above, 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 planet's mantle, early in Earth's creation. In 2017, an international group of scientists, established that gold "came to the Earth's surface from the deepest regions of our planet",[65] the mantle, evidenced by their findings at Deseado Massif in the Argentinian Patagonia.[66][clarification needed]

Occurrence

On Earth, gold is found in ores in rock formed from the Precambrian time onward.[67] 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.

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.[68] These are called lode deposits. The metal in a native state is also found in the form of free flakes, grains or larger nuggets[67] 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 (Au2Bi) and antimonide aurostibite (AuSb2). Gold also occurs in rare alloys with copper, lead, and mercury: the minerals auricupride (Cu3Au), novodneprite (AuPb3) and weishanite ((Au,Ag)3Hg2).

Recent research 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.[69]

Another recent 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 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.[70]

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) attributed to wind-blown dust and/or rivers. At 10 parts per quadrillion the Earth's oceans would hold 15,000 tonnes of gold.[71] 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.[72] 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.[73] 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.[74]

History

 
Oldest golden artifacts in the world (4600 BC - 4200 BC) from Varna necropolis, Bulgaria - grave offerings on exposition in Varna Museum.
 
An Indian tribute-bearer at Apadana, from the Achaemenid satrapy of Hindush, carrying gold on a yoke, circa 500 BC.[75]
 
The Muisca raft, between circa 600-1600 AD. The figure refers to the ceremony of the legend of El Dorado. The zipa used to cover his body in gold dust, and from his raft, he offered treasures to the Guatavita goddess in the middle of the sacred lake. This old Muisca tradition became the origin of the legend of El Dorado.
This Muisca raft figure is on display in the Gold Museum, Bogotá, Colombia.

The earliest recorded metal employed by humans appears to be gold, which can be found free or "native". Small amounts of natural gold have been found in Spanish caves used during the late Paleolithic period, c. 40,000 BC.[76]

The oldest gold artifacts in the world are from Bulgaria and are dating back to the 5th millennium BC (4,600 BC to 4,200 BC), such as those found in the Varna Necropolis near Lake Varna and the Black Sea coast, thought to be the earliest "well-dated" finding of gold artifacts in history.[77][67][78][79] Several prehistoric Bulgarian finds are considered no less old – the golden treasures of Hotnitsa, Durankulak, artifacts from the Kurgan settlement of Yunatsite near Pazardzhik, the golden treasure Sakar, as well as beads and gold jewelry found in the Kurgan settlement of ProvadiaSolnitsata (“salt pit”). However, Varna gold is most often called the oldest since this treasure is the largest and most diverse.[80]

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.[81] 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.[82] Gold artifacts such as the golden hats and the Nebra disk appeared in Central Europe from the 2nd millennium BC Bronze Age.

The oldest known map of a gold mine was drawn in the 19th Dynasty of Ancient Egypt (1320–1200 BC), whereas the first written reference to gold was recorded in the 12th Dynasty around 1900 BC.[83] Egyptian hieroglyphs from as early as 2600 BC describe gold, which King Tushratta of the Mitanni claimed was "more plentiful than dirt" in Egypt.[84] Egypt and especially Nubia had the resources to make them major gold-producing areas for much of history. One of the earliest known maps, known as the Turin Papyrus Map, shows the plan of a gold mine in Nubia together with indications of the local geology. The primitive working methods are described by both Strabo and Diodorus Siculus, and included fire-setting. Large mines were also present across the Red Sea in what is now Saudi Arabia.

 
Ancient golden Kritonios Crown, funerary or marriage material, 370–360 BC. From a grave in Armento, Basilicata

Gold is mentioned in the Amarna letters numbered 19[85] and 26[86] from around the 14th century BC.[87][88]

Gold is mentioned frequently in the Old Testament, starting with Genesis 2:11 (at Havilah), the story of the golden calf, and many parts of the temple including the Menorah and the golden altar. In the New Testament, it is included with the gifts of the magi in the first chapters of Matthew. The Book of Revelation 21:21 describes the city of New Jerusalem as having streets "made of pure gold, clear as crystal". Exploitation of gold in the south-east corner of the Black Sea is said to date from the time of Midas, and this gold was important in the establishment of what is probably the world's earliest coinage in Lydia around 610 BC.[89] The legend of the golden fleece dating from eighth century BCE may refer to the use of fleeces to trap gold dust from placer deposits in the ancient world. From the 6th or 5th century BC, the Chu (state) circulated the Ying Yuan, one kind of square gold coin.

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

During Mansa Musa's (ruler of the Mali Empire from 1312 to 1337) hajj to Mecca in 1324, he passed through Cairo in July 1324, and was reportedly accompanied by a camel train that included thousands of people and nearly a hundred camels where he gave away so much gold that it depressed the price in Egypt for over a decade, causing high inflation.[90] 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 [...].

— Chihab Al-Umari, Kingdom of Mali[91]
 
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 (169.2 g (5.97 oz); 58 mm (2.3 in)).[92]

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.[93] 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.[94] El Dorado is applied to a legendary story in which precious stones were found in fabulous abundance along with gold coins. The concept of El Dorado underwent several transformations, and eventually accounts of the previous myth were also combined with those of a legendary lost city. El Dorado, was the term used by the Spanish Empire to describe a mythical tribal chief (zipa) of the Muisca native people in Colombia, who, as an initiation rite, covered himself with gold dust and submerged in Lake Guatavita. The legends surrounding El Dorado changed over time, as it went from being a man, to a city, to a kingdom, and then finally to an empire.

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".[95] From the late 15th to early 19th centuries, European trade in the region was primarily focused in gold, along with ivory and slaves.[96] 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.[97] 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.[98]

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

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

75% of the presently accounted for gold has been extracted since 1910, two-thirds since 1950.

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.[99] Their symbol for gold was the circle with a point at its center (☉), which was also the astrological symbol and the ancient Chinese character for the Sun.

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

Etymology

 
An early mention of gold in the Beowulf

"Gold" is cognate with similar words in many Germanic languages, deriving via Proto-Germanic *gulþą from Proto-Indo-European *ǵʰelh₃- ("to shine, to gleam; to be yellow or green").[100][101]

The symbol Au is from the Latin: aurum, the Latin word for "gold".[102] The Proto-Indo-European ancestor of aurum was *h₂é-h₂us-o-, meaning "glow". This word is derived from the same root (Proto-Indo-European *h₂u̯es- "to dawn") as *h₂éu̯sōs, the ancestor of the Latin word Aurora, "dawn".[103] This etymological relationship is presumably behind the frequent claim in scientific publications that aurum meant "shining dawn".[104]

Culture

 
Gold crafts from the Philippines prior to Western contact.

In popular culture gold is a high standard of excellence, often used in awards.[44] Great achievements are frequently rewarded with gold, in the form of gold medals, gold trophies and other decorations. Winners of athletic events and other graded competitions are usually awarded a gold medal. Many awards such as the Nobel Prize are made from gold as well. Other award statues and prizes are depicted in gold or are gold plated (such as the Academy Awards, the Golden Globe Awards, the Emmy Awards, the Palme d'Or, and the British Academy Film Awards).[105]

Aristotle in his ethics used gold symbolism when referring to what is now known as the golden mean. Similarly, gold is associated with perfect or divine principles, such as in the case of the golden ratio and the golden rule. Gold is further associated with the wisdom of aging and fruition. The fiftieth wedding anniversary is golden. A person's most valued or most successful latter years are sometimes considered "golden years". The height of a civilization is referred to as a golden age.[106]

Religion

 
The Agusan image, depicting a deity from northeast Mindanao.

In some forms of Christianity and Judaism, gold has been associated both with the sacred and evil. In the Book of Exodus, the Golden Calf is a symbol of idolatry, while in the Book of Genesis, Abraham was said to be rich in gold and silver, and Moses was instructed to cover the Mercy Seat of the Ark of the Covenant with pure gold. In Byzantine iconography the halos of Christ, Virgin Mary and the saints are often golden.[107]

In Islam,[108] gold (along with silk)[109][110] is often cited as being forbidden for men to wear.[111] Abu Bakr al-Jazaeri, quoting a hadith, said that "[t]he wearing of silk and gold are forbidden on the males of my nation, and they are lawful to their women".[112] This, however, has not been enforced consistently throughout history, e.g. in the Ottoman Empire.[113] Further, small gold accents on clothing, such as in embroidery, may be permitted.[114]

In ancient Greek religion and mythology, Theia was seen as the goddess of gold, silver and other gems.[115]

According to Christopher Columbus, those who had something of gold were in possession of something of great value on Earth and a substance to even help souls to paradise.[116]

Wedding rings are typically made of gold. It is long lasting and unaffected by the passage of time and may aid in the ring symbolism of eternal vows before God and the perfection the marriage signifies. In Orthodox Christian wedding ceremonies, the wedded couple is adorned with a golden crown (though some opt for wreaths, instead) during the ceremony, an amalgamation of symbolic rites.

On 24 August 2020, Israeli archaeologists discovered a trove of early Islamic gold coins near the central city of Yavne. Analysis of the extremely rare collection of 425 gold coins indicated that they were from the late 9th century. Dating to around 1,100 years back, the gold coins were from the Abbasid Caliphate.[117]

Production

 
Time trend of gold production

According to the United 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.[118]

Mining and prospecting

 
A miner underground at Pumsaint gold mine, Wales; c. 1938.
 
Grasberg mine, Indonesia is the world's largest gold mine.

Since the 1880s, South Africa has been the source of a large proportion of the world's gold supply, and about 22% of the gold presently accounted is from South Africa. Production in 1970 accounted for 79% of the world supply, about 1,480 tonnes. In 2007 China (with 276 tonnes) overtook South Africa as the world's largest gold producer, the first time since 1905 that South Africa had not been the largest.[119]

In 2020, China was the world's leading gold-mining country, followed in order by Russia, Australia, the United States, Canada, and Ghana.[8]

 
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 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.[120][121][122]

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 5–7 km (3.1–4.3 mi) thick layer of archean rocks located, in most places, deep under the Free State, Gauteng and surrounding provinces.[123] 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.[63][123] From these surface exposures the basin dips extensively, requiring some of the mining to occur at depths of nearly 4,000 m (13,000 ft), 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.[123]

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.

 
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.[124] The first major gold strike in the United States occurred in a small north Georgia town called Dahlonega.[125] 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.[126]

Extraction and refining

 
Gold Nuggets found in Arizona.

Gold extraction is most economical in large, easily mined deposits. Ore grades as little as 0.5 parts per million (ppm) can be economical. Typical ore grades in open-pit mines are 1–5 ppm; ore grades in underground or hard rock mines are usually at least 3 ppm. Because ore grades of 30 ppm are usually needed before gold is visible to the naked eye, in most gold mines the gold is invisible.

The average gold mining and extraction costs were about $317 per troy ounce in 2007, but these can vary widely depending on mining type and ore quality; global mine production amounted to 2,471.1 tonnes.[127]

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.[128][129] 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.[130]

As of 2020, the amount of carbon dioxide CO2 produced in mining a kilogram of gold is 16 tonnes, while recycling a kilogram of gold produces 53 kilograms of CO2 equivalent. Approximately 30 percent of the global gold supply is recycled and not mined as of 2020.[131]

Corporations are starting to adopt gold recycling including jewelry companies such as Generation Collection and computer companies including Dell.[132]

Consumption

Gold jewelry consumption by country in tonnes[133][134][135]
Country 2009 2010 2011 2012 2013
  India 442.37 745.70 986.3 864 974
  China 376.96 428.00 921.5 817.5 1120.1
  United States 150.28 128.61 199.5 161 190
  Turkey 75.16 74.07 143 118 175.2
  Saudi Arabia 77.75 72.95 69.1 58.5 72.2
  Russia 60.12 67.50 76.7 81.9 73.3
  United Arab Emirates 67.60 63.37 60.9 58.1 77.1
  Egypt 56.68 53.43 36 47.8 57.3
  Indonesia 41.00 32.75 55 52.3 68
  United Kingdom 31.75 27.35 22.6 21.1 23.4
Other Persian Gulf Countries 24.10 21.97 22 19.9 24.6
  Japan 21.85 18.50 −30.1 7.6 21.3
  South Korea 18.83 15.87 15.5 12.1 17.5
  Vietnam 15.08 14.36 100.8 77 92.2
  Thailand 7.33 6.28 107.4 80.9 140.1
Total 1466.86 1770.71 2786.12 2477.7 3126.1
Other Countries 251.6 254.0 390.4 393.5 450.7
World Total 1718.46 2024.71 3176.52 2871.2 3576.8

The consumption of gold produced in the world is about 50% in jewelry, 40% in investments, and 10% in industry.[10][136]

According to the World Gold Council, China was the world's largest single consumer of gold in 2013, overtaking India.[137]

Pollution

Gold production is associated with contribution to hazardous pollution.[138][139]

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[140] 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.[141][142] Up to thirty tons of used ore can dumped as waste for producing one troy ounce of gold.[143] 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 are long-term, highly hazardous wastes second only to nuclear waste dumps.[143]

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.[144] 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 causes incurable brain function damage and severe retardation.[145]

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.[146]

Monetary use

 
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,[147] 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.[89] 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.[148] From an earlier preference in using silver, European economies re-established the minting of gold as coinage during the thirteenth and fourteenth centuries.[149]

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.[150]

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.[151] 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,[152] for hardness (American gold coins for circulation after 1837 contain an alloy of 0.900 fine gold, or 21.6 kt).[153]

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

The ISO 4217 currency code of gold is XAU.[154] Many holders of gold store it in form of bullion coins or bars as a hedge against inflation or other economic disruptions, though its efficacy as such has been questioned; historically, it has not proven itself reliable as a hedging instrument.[155] 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).[156]

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.[157]

Price

 
Gold price history in 1960–2020.

As of September 2017, gold is valued at around $42 per gram ($1,300 per troy ounce).

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.[158]

History

Historically gold coinage was widely used as currency; when paper money was introduced, it typically was a receipt redeemable for gold coin or bullion. In a monetary system known as the gold standard, a certain weight of gold was given the name of a unit of currency. For a long period, the United States government set the value of the US dollar so that one troy ounce was equal to $20.67 ($0.665 per gram), but in 1934 the dollar was devalued to $35.00 per troy ounce ($0.889/g). By 1961, it was becoming hard to maintain this price, and a pool of US and European banks agreed to manipulate the market to prevent further currency devaluation against increased gold demand.[159]

On 17 March 1968, economic circumstances[clarification needed] caused the collapse of the gold pool, and a two-tiered pricing scheme was established whereby gold was still used to settle international accounts at the old $35.00 per troy ounce ($1.13/g) but the price of gold on the private market was allowed to fluctuate; this two-tiered pricing system was abandoned in 1975 when the price of gold was left to find its free-market level.[citation needed] Central banks still hold historical gold reserves as a store of value although the level has generally been declining.[citation needed] The largest gold depository in the world is that of the U.S. Federal Reserve Bank in New York, which holds about 3%[160] of the gold known to exist and accounted for today, as does the similarly laden U.S. Bullion Depository at Fort Knox. In 2005 the World Gold Council estimated total global gold supply to be 3,859 tonnes and demand to be 3,754 tonnes, giving a surplus of 105 tonnes.[161]

After 15 August 1971 Nixon shock, the price began to greatly increase,[162] 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).[163] Prices increased rapidly from 2001, but the 1980 high was not exceeded until 3 January 2008, when a new maximum of $865.35 per troy ounce was set.[164] Another record price was set on 17 March 2008, at $1023.50 per troy ounce ($32.91/g).[164]

In late 2009, gold markets experienced renewed momentum upwards due to increased demand and a weakening US dollar.[citation needed] On 2 December 2009, gold reached a new high closing at $1,217.23.[165] Gold further rallied hitting new highs in May 2010 after the European Union debt crisis prompted further purchase of gold as a safe asset.[166][167] On 1 March 2011, gold hit a new all-time high of $1432.57, based on investor concerns regarding ongoing unrest in North Africa as well as in the Middle East.[168]

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,[169] prompting speculation that the long secular bear market had ended and a bull market had returned.[170] 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 complexive growth of 59% from August 2018 to October 2020, a period during which it outplaced the Nasdaq total return of 54%.[171]

Gold futures are traded on the COMEX exchange.[172] These contacts are priced in USD per troy ounce (1 troy ounce = 31.1034768 grams).[173] Below are the CQG contract specifications outlining the futures contracts:

Contract Specifications[172]
Gold (GCA)
Exchange: COMEX
Sector: Metal
Tick Size: 0.1
Tick Value: 10 USD
BPV: 100
Denomination: USD
Decimal Place: 1

Medicinal uses

Medicinal applications of gold and its complexes have a long history dating back thousands of years.[174] Several gold complexes have been applied to treat rheumatoid arthritis, the most frequently used being aurothiomalate, aurothioglucose, and auranofin. Both gold(I) and gold(III) compounds have been investigated as possible anti-cancer drugs. For gold(III) complexes, reduction to gold(0/I) under physiological conditions has to be considered. Stable complexes can be generated using different types of bi-, tri-, and tetradentate ligand systems, and their efficacy has been demonstrated in vitro and in vivo.[175]

Other applications

Jewelry

 
Moche gold necklace depicting feline heads. Larco Museum Collection, Lima, Peru.
 
A 21.5k yellow gold pendant watch so-called "Boule de Genève" (Geneva ball), ca. 1890.

Because of the softness of pure (24k) gold, it is usually alloyed with base 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 or other base metals or silver or palladium in the alloy.[24] Nickel is toxic, and its release from nickel white gold is controlled by legislation in Europe.[24] Palladium-gold alloys are more expensive than those using nickel.[176] High-karat white gold alloys are more resistant to corrosion than are either pure silver or sterling silver. The Japanese craft of Mokume-gane exploits the color contrasts between laminated colored gold alloys to produce decorative wood-grain effects.

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

Gold solder is used for joining the components of gold jewelry by high-temperature hard soldering or brazing. If the work is to be of hallmarking quality, the gold solder alloy must match the fineness (purity) 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,[10] 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 2 dollars 82 cents. 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.[177] (Prices updated to November 2022)

Though gold is attacked by free chlorine, its good conductivity and general resistance to oxidation and corrosion in other environments (including resistance to non-chlorinated acids) has led to its widespread industrial use in the electronic era as a thin-layer coating on electrical connectors, thereby ensuring good connection. For example, gold is used in the connectors of the more expensive electronics cables, such as audio, video and USB cables. The benefit of using gold over other connector metals such as tin in these applications has been debated; gold connectors are often criticized by audio-visual experts as unnecessary for most consumers and seen as simply a marketing ploy. However, the use of gold in other applications in electronic sliding contacts in highly humid or corrosive atmospheres, and in use for contacts with a very high failure cost (certain computers, communications equipment, spacecraft, jet aircraft engines) remains very common.[178]

Besides sliding electrical contacts, gold is also used in electrical contacts because of its resistance to corrosion, electrical conductivity, ductility and lack of toxicity.[179] 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.[180] Gold is highly conductive to electricity, and has been used for electrical wiring in some high-energy applications (only silver and copper are more conductive per volume, but gold has the advantage of corrosion resistance). For example, gold electrical wires were used during some of the Manhattan Project's atomic experiments, but large high-current silver wires were used in the calutron isotope separator magnets in the project.

It is estimated that 16% of the world's presently-accounted-for gold and 22% of the world's silver is contained in electronic technology in Japan.[181]

Medicine

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)[182] and known to Dioscorides.[183][184] 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. Even some modern esotericists and forms of alternative medicine assign metallic gold a healing power.

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).[185]

The apparent paradox of the actual toxicology of the substance suggests the possibility of serious gaps in the understanding of the action of gold in physiology.[186] 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). Some gold salts do have anti-inflammatory properties and at present two are still used as pharmaceuticals in the treatment of arthritis and other similar conditions in the US (sodium aurothiomalate and auranofin). 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.[187]

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.[188] In ultrathin sections of tissues viewed by electron microscopy, the immunogold labels appear as extremely dense round spots at the position of the antigen.[189]

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.[190]

The isotope gold-198 (half-life 2.7 days) is used in nuclear medicine, in some cancer treatments and for treating other diseases.[191][192]

Cuisine

 
Cake with gold decoration served at the Amstel Hotel, Amsterdam
  • Gold can be used in food and has the E number 175.[193] 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.[194]
  • Gold leaf, flake or dust is used on and in some gourmet foods, notably sweets and drinks as decorative ingredient.[195] Gold flake was used by the nobility in medieval Europe as a decoration in food and drinks,[196] in the form of leaf, flakes or dust, either to demonstrate the host's wealth or in the belief that something that valuable and rare must be beneficial for one's health.[citation needed]
  • Danziger Goldwasser (German: Gold water of Danzig) or Goldwasser (English: Goldwater) is a traditional German herbal liqueur[197] produced in what is today Gdańsk, Poland, and Schwabach, Germany, and contains flakes of gold leaf. There are also some expensive (c. $1000) cocktails which contain flakes of gold leaf. However, since metallic gold is inert to all body chemistry, it has no taste, it provides no nutrition, and it leaves the body unaltered.[198]
  • Vark is a foil composed of a pure metal that is sometimes gold,[199] and is used for garnishing sweets in South Asian cuisine.

Miscellanea

 
Mirror for the James Webb Space Telescope coated in gold to reflect infrared light
 
Kamakshi Amman Temple with golden roof, Kanchipuram.
  • Gold produces a deep, intense red color when used as a coloring agent in cranberry glass.
  • In photography, gold toners are used to shift the color of silver bromide black-and-white prints towards brown or blue tones, or to increase their stability. Used on sepia-toned prints, gold toners produce red tones. Kodak published formulas for several types of gold toners, which use gold as the chloride.[200]
  • 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.[201]
  • 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.[202]
  • 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.[203]
  • Gold, when dispersed in nanoparticles, can act as a heterogeneous catalyst of chemical reactions.

Toxicity

Pure metallic (elemental) gold is non-toxic and non-irritating when ingested[204] and is sometimes used as a food decoration in the form of gold leaf.[205] 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.[206][207] 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.[208] Despite this, gold is a relatively non-potent contact allergen, in comparison with metals like nickel.[209]

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.[210]

See also

 
Iron pyrite or "fool's gold"

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Further reading

  • Bachmann, H. G. The lure of gold : an artistic and cultural history (2006) online
  • Bernstein, Peter L. The Power of Gold: The History of an Obsession (2000) online
  • Brands, H.W. The Age of Gold: The California Gold Rush and the New American Dream (2003) excerpt
  • Buranelli, Vincent. Gold : an illustrated history (1979) online' wide-ranging popular history
  • Cassel, Gustav. "The restoration of the gold standard." Economica 9 (1923): 171–185. 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) online
  • Hart, Matthew, 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
  • Johnson, Harry G. "The gold rush of 1968 in retrospect and prospect". American Economic Review 59.2 (1969): 344–348. online
  • Kwarteng, Kwasi. War and Gold: A Five-Hundred-Year History of Empires, Adventures, and Debt (2014) online
  • Vilar, Pierre. A History of Gold and Money, 1450–1920 (1960). online
  • Vilches, Elvira. New World Gold: Cultural Anxiety and Monetary Disorder in Early Modern Spain (2010).

External links

gold, this, article, about, element, other, uses, disambiguation, element, redirects, here, anthology, element, anthology, chemical, element, with, symbol, from, latin, aurum, atomic, number, this, makes, higher, atomic, number, elements, that, occur, naturall. This article is about the element For other uses see Gold disambiguation Element 79 redirects here For the anthology see Element 79 anthology Gold is a chemical element with the symbol Au from Latin aurum and atomic number 79 This makes it one of the higher atomic number elements that occur naturally It is a bright slightly orange yellow dense soft malleable and ductile metal in a pure form Chemically gold is a transition metal and a group 11 element It is one of the least reactive chemical elements and is solid under standard conditions Gold often occurs in free elemental native state as nuggets or grains in rocks veins and alluvial deposits It occurs in a solid solution series with the native element silver as electrum naturally alloyed with other metals like copper and palladium and mineral inclusions such as within pyrite Less commonly it occurs in minerals as gold compounds often with tellurium gold tellurides Gold 79AuGoldAppearancemetallic yellowStandard atomic weight Ar Au 196 966570 0 000004196 97 0 01 abridged 1 Gold in the periodic tableHydrogen HeliumLithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine NeonSodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine ArgonPotassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine KryptonRubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine XenonCaesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury element Thallium Lead Bismuth Polonium Astatine RadonFrancium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson Ag Au Rgplatinum gold mercuryAtomic number Z 79Groupgroup 11Periodperiod 6Block d blockElectron configuration Xe 4f14 5d10 6s1Electrons per shell2 8 18 32 18 1Physical propertiesPhase at STPsolidMelting point1337 33 K 1064 18 C 1947 52 F Boiling point3243 K 2970 C 5378 F Density near r t 19 3 g cm3when liquid at m p 17 31 g cm3Heat of fusion12 55 kJ molHeat of vaporization342 kJ molMolar heat capacity25 418 J mol K Vapor pressureP Pa 1 10 100 1 k 10 k 100 kat T K 1646 1814 2021 2281 2620 3078Atomic propertiesOxidation states 3 2 1 0 2 1 2 3 5 an amphoteric oxide ElectronegativityPauling scale 2 54Ionization energies1st 890 1 kJ mol2nd 1980 kJ molAtomic radiusempirical 144 pmCovalent radius136 6 pmVan der Waals radius166 pmSpectral lines of goldOther propertiesNatural occurrenceprimordialCrystal structure face centered cubic fcc Speed of sound thin rod2030 m s at r t Thermal expansion14 2 µm m K at 25 C Thermal conductivity318 W m K Electrical resistivity22 14 nW m at 20 C Magnetic orderingdiamagnetic 3 Molar magnetic susceptibility 28 0 10 6 cm3 mol at 296 K 4 Tensile strength120 MPaYoung s modulus79 GPaShear modulus27 GPaBulk modulus180 GPa 5 Poisson ratio0 4Mohs hardness2 5Vickers hardness188 216 MPaBrinell hardness188 245 MPaCAS Number7440 57 5HistoryNamingfrom Latin aurum meaning goldDiscoveryIn the Middle East before 6000 BCE Symbol Au from Latin aurumMain isotopes of goldveIso tope Decayabun dance half life t1 2 mode pro duct195Au syn 186 01 d e 195Pt196Au syn 6 165 d b 196Ptb 196Hg197Au 100 stable198Au syn 2 69464 d b 198Hg199Au syn 3 139 d b 199Hg Category Goldviewtalkedit referencesGold 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 6 7 gold is a precious metal that has been used for coinage jewelry and other arts throughout recorded history In the past a gold standard was often implemented as a monetary policy Gold coins ceased to be minted as a circulating currency in the 1930s and the world gold standard was abandoned for a fiat currency system after the Nixon shock measures of 1971 In 2020 the world s largest gold producer was China followed by Russia and Australia 8 A total of around 201 296 tonnes of gold exists above ground as of 2020 update 9 This is equal to a cube with each side measuring roughly 21 7 meters 71 ft The world consumption of new gold produced is about 50 in jewelry 40 in investments and 10 in industry 10 Gold s high malleability ductility resistance to corrosion and most other chemical reactions and 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 production of colored glass gold leafing and tooth restoration Certain gold salts are still used as anti inflammatories in medicine Contents 1 Characteristics 1 1 Color 1 2 Isotopes 1 2 1 Synthesis 2 Chemistry 2 1 Rare oxidation states 3 Origin 3 1 Gold production in the universe 3 2 Asteroid origin theories 3 3 Mantle return theories 4 Occurrence 4 1 Seawater 5 History 5 1 Etymology 5 2 Culture 5 2 1 Religion 6 Production 6 1 Mining and prospecting 6 2 Extraction and refining 6 3 Consumption 6 4 Pollution 7 Monetary use 7 1 Price 7 2 History 7 3 Medicinal uses 8 Other applications 8 1 Jewelry 8 2 Electronics 8 3 Medicine 8 4 Cuisine 8 5 Miscellanea 9 Toxicity 10 See also 11 References 12 Further reading 13 External linksCharacteristics Gold can be drawn into a monatomic wire and then stretched more before it breaks 11 A gold nugget of 5 mm 0 20 in in size can be hammered into a gold foil of about 0 5 m2 5 4 sq ft in area Gold is the most malleable of all metals It can be drawn into a wire of single atom width and then stretched considerably before it breaks 11 Such nanowires distort via formation reorientation and migration of dislocations and crystal twins without noticeable hardening 12 A single gram of gold can be beaten into a sheet of 1 square metre 11 sq ft and an avoirdupois ounce into 300 square feet 28 m2 Gold leaf can be beaten thin enough to become semi transparent The transmitted light appears greenish blue because gold strongly reflects yellow and red 13 Such semi transparent sheets also strongly reflect infrared light making them useful as infrared radiant heat shields in visors of heat resistant suits and in sun visors for spacesuits 14 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 counterfeiting of gold bars such as by plating a tungsten bar with gold 15 16 17 18 or taking an existing gold bar drilling holes and replacing the removed gold with tungsten rods 19 By comparison the density of lead is 11 34 g cm3 and that of the densest element osmium is 22 588 0 015 g cm3 20 Color Main article Colored gold Different colors of Ag Au Cu alloys Whereas most metals are gray or silvery white gold is slightly reddish yellow 21 This color is determined by the frequency of plasma oscillations among the metal s valence electrons in the ultraviolet range for most metals but in the visible range for gold due to relativistic effects affecting the orbitals around gold atoms 22 23 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 24 Colloidal gold used by electron microscopists is red if the particles are small larger particles of colloidal gold are blue 25 Isotopes Main article Isotopes of gold Gold has only one stable isotope 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 195 Au with a half life of 186 1 days The least stable is 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 a decay and b decay The exceptions are 195 Au which decays by electron capture and 196 Au which decays most often by electron capture 93 with a minor b decay path 7 26 All of gold s radioisotopes with atomic masses above 197 decay by b decay 27 At least 32 nuclear isomers have also been characterized ranging in atomic mass from 170 to 200 Within that range only 178 Au 180 Au 181 Au 182 Au and 188 Au do not have isomers Gold s most stable isomer is 198m2 Au with a half life of 2 27 days Gold s least stable isomer is 177m2 Au with a half life of only 7 ns 184m1 Au has three decay paths b decay isomeric transition and alpha decay No other isomer or isotope of gold has three decay paths 27 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 28 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 29 In 1980 Glenn Seaborg transmuted several thousand atoms of bismuth into gold at the Lawrence Berkeley Laboratory 30 31 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 32 Chemistry Gold III chloride solution in water Although gold is the most noble of the noble metals 33 34 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 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 35 Au III referred to as the auric is a common oxidation state and is illustrated by gold III chloride 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 36 and up to 100 C is resistant to attack from ozone 37 A u O 2 displaystyle mathrm Au mathrm O 2 neq A u O 3 t lt 100 C displaystyle mathrm Au mathrm O 3 overset underset t lt 100 circ text C neq Some free halogens react with gold 38 Gold is strongly attacked by fluorine at dull red heat 39 to form gold III fluoride AuF3 Powdered gold reacts with chlorine at 180 C to form gold III chloride AuCl3 40 Gold reacts with bromine at 140 C to form gold III bromide AuBr3 but reacts only very slowly with iodine to form gold I iodide AuI 2 Au 3 F 2 t 2 AuF 3 displaystyle ce 2 Au 3 F2 gt t 2 AuF3 2 Au 3 Cl 2 t 2 AuCl 3 displaystyle ce 2 Au 3 Cl2 gt t 2 AuCl3 2 Au 2 Br 2 t AuBr 3 AuBr displaystyle ce 2 Au 2 Br2 gt t AuBr3 AuBr 2 Au I 2 t 2 AuI displaystyle ce 2 Au I2 gt t 2 AuI Gold does not react with sulfur directly 41 but gold III sulfide can be made by passing hydrogen sulfide through a dilute solution of gold III chloride or chlorauric acid 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 24 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 AuCl 4 ions or chloroauric acid thereby enabling further oxidation 2 Au 6 H 2 SeO 4 200 C Au 2 SeO 4 3 3 H 2 SeO 3 3 H 2 O displaystyle ce 2Au 6H2SeO4 gt 200 circ C Au2 SeO4 3 3H2SeO3 3H2O Au 4 HCl HNO 3 H AuCl 4 NO 2 H 2 O displaystyle ce Au 4HCl HNO3 gt H AuCl4 NO uparrow 2H2O 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 41 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 Au anion Caesium auride CsAu for example crystallizes in the caesium chloride motif 42 rubidium potassium and tetramethylammonium aurides are also known 43 Gold has the highest electron affinity of any metal at 222 8 kJ mol making Au a stable species 44 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 45 Gold II compounds are usually diamagnetic with Au Au bonds such as Au CH2 2P C6H5 2 2Cl2 The evaporation of a solution of Au OH 3 in concentrated H2SO4 produces red crystals of gold II sulfate Au2 SO4 2 Originally thought to be a mixed valence compound it has been shown to contain Au4 2 cations analogous to the better known mercury I ion Hg2 2 46 47 A gold II complex the tetraxenonogold II cation which contains xenon as a ligand occurs in AuXe4 Sb2F11 2 48 Gold pentafluoride along with its derivative anion AuF 6 and its difluorine complex gold heptafluoride is the sole example of gold V the highest verified oxidation state 49 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 43 In some cases gold has a fractional oxidation state A representative example is the octahedral species Au P C6H5 3 2 6 OriginGold production in the universe 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 is thought to have been produced in supernova nucleosynthesis and from the collision of neutron stars 50 and to have been present in the dust from which the Solar System formed 51 Traditionally gold in the universe is thought to have formed by the r process rapid neutron capture in supernova nucleosynthesis 52 but more recently it has been suggested that gold and other elements heavier than iron may also be produced in quantity by the r process in the collision of neutron stars 53 In both cases satellite spectrometers at first only indirectly detected the resulting gold 54 However in August 2017 the spectroscopic signatures of heavy elements including gold were observed by electromagnetic observatories in the GW170817 neutron star merger event after gravitational wave detectors confirmed the event as a neutron star merger 55 Current astrophysical models suggest that this single neutron star merger event generated between 3 and 13 Earth 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 56 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 most of the gold that is in the Earth s crust and mantle has in one model thought to have been delivered to Earth later by asteroid impacts during the Late Heavy Bombardment about 4 billion years ago 57 58 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 59 60 61 62 However this scenario is now questioned The gold bearing Witwatersrand rocks were laid down between 700 and 950 million years before the Vredefort impact 63 64 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 300 km 190 mi 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 64 Mantle return theories Notwithstanding the impact above 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 planet s mantle early in Earth s creation In 2017 an international group of scientists established that gold came to the Earth s surface from the deepest regions of our planet 65 the mantle evidenced by their findings at Deseado Massif in the Argentinian Patagonia 66 clarification needed OccurrenceOn Earth gold is found in ores in rock formed from the Precambrian time onward 67 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 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 68 These are called lode deposits The metal in a native state is also found in the form of free flakes grains or larger nuggets 67 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 Au2Bi and antimonide aurostibite AuSb2 Gold also occurs in rare alloys with copper lead and mercury the minerals auricupride Cu3Au novodneprite AuPb3 and weishanite Au Ag 3Hg2 Recent research 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 69 Another recent 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 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 70 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 attributed to wind blown dust and or rivers At 10 parts per quadrillion the Earth s oceans would hold 15 000 tonnes of gold 71 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 72 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 73 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 74 History Oldest golden artifacts in the world 4600 BC 4200 BC from Varna necropolis Bulgaria grave offerings on exposition in Varna Museum An Indian tribute bearer at Apadana from the Achaemenid satrapy of Hindush carrying gold on a yoke circa 500 BC 75 The Muisca raft between circa 600 1600 AD The figure refers to the ceremony of the legend of El Dorado The zipa used to cover his body in gold dust and from his raft he offered treasures to the Guatavita goddess in the middle of the sacred lake This old Muisca tradition became the origin of the legend of El Dorado This Muisca raft figure is on display in the Gold Museum Bogota Colombia The earliest recorded metal employed by humans appears to be gold which can be found free or native Small amounts of natural gold have been found in Spanish caves used during the late Paleolithic period c 40 000 BC 76 The oldest gold artifacts in the world are from Bulgaria and are dating back to the 5th millennium BC 4 600 BC to 4 200 BC such as those found in the Varna Necropolis near Lake Varna and the Black Sea coast thought to be the earliest well dated finding of gold artifacts in history 77 67 78 79 Several prehistoric Bulgarian finds are considered no less old the golden treasures of Hotnitsa Durankulak artifacts from the Kurgan settlement of Yunatsite near Pazardzhik the golden treasure Sakar as well as beads and gold jewelry found in the Kurgan settlement of Provadia Solnitsata salt pit However Varna gold is most often called the oldest since this treasure is the largest and most diverse 80 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 81 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 82 Gold artifacts such as the golden hats and the Nebra disk appeared in Central Europe from the 2nd millennium BC Bronze Age The oldest known map of a gold mine was drawn in the 19th Dynasty of Ancient Egypt 1320 1200 BC whereas the first written reference to gold was recorded in the 12th Dynasty around 1900 BC 83 Egyptian hieroglyphs from as early as 2600 BC describe gold which King Tushratta of the Mitanni claimed was more plentiful than dirt in Egypt 84 Egypt and especially Nubia had the resources to make them major gold producing areas for much of history One of the earliest known maps known as the Turin Papyrus Map shows the plan of a gold mine in Nubia together with indications of the local geology The primitive working methods are described by both Strabo and Diodorus Siculus and included fire setting Large mines were also present across the Red Sea in what is now Saudi Arabia Ancient golden Kritonios Crown funerary or marriage material 370 360 BC From a grave in Armento Basilicata Gold is mentioned in the Amarna letters numbered 19 85 and 26 86 from around the 14th century BC 87 88 Gold is mentioned frequently in the Old Testament starting with Genesis 2 11 at Havilah the story of the golden calf and many parts of the temple including the Menorah and the golden altar In the New Testament it is included with the gifts of the magi in the first chapters of Matthew The Book of Revelation 21 21 describes the city of New Jerusalem as having streets made of pure gold clear as crystal Exploitation of gold in the south east corner of the Black Sea is said to date from the time of Midas and this gold was important in the establishment of what is probably the world s earliest coinage in Lydia around 610 BC 89 The legend of the golden fleece dating from eighth century BCE may refer to the use of fleeces to trap gold dust from placer deposits in the ancient world From the 6th or 5th century BC the Chu state circulated the Ying Yuan one kind of square gold coin In Roman metallurgy new methods for extracting gold on a large scale were developed by introducing hydraulic mining methods especially in Hispania from 25 BC onwards and in Dacia from 106 AD onwards One of their largest mines was at Las Medulas in Leon where seven long aqueducts enabled them to sluice most of a large alluvial deposit The mines at Rosia Montană in Transylvania were also very large and until very recently still mined by opencast methods They also exploited smaller deposits in Britain such as placer and hard rock deposits at Dolaucothi The various methods they used are well described by Pliny the Elder in his encyclopedia Naturalis Historia written towards the end of the first century AD During Mansa Musa s ruler of the Mali Empire from 1312 to 1337 hajj to Mecca in 1324 he passed through Cairo in July 1324 and was reportedly accompanied by a camel train that included thousands of people and nearly a hundred camels where he gave away so much gold that it depressed the price in Egypt for over a decade causing high inflation 90 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 Chihab Al Umari Kingdom of Mali 91 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 169 2 g 5 97 oz 58 mm 2 3 in 92 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 93 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 94 El Dorado is applied to a legendary story in which precious stones were found in fabulous abundance along with gold coins The concept of El Dorado underwent several transformations and eventually accounts of the previous myth were also combined with those of a legendary lost city El Dorado was the term used by the Spanish Empire to describe a mythical tribal chief zipa of the Muisca native people in Colombia who as an initiation rite covered himself with gold dust and submerged in Lake Guatavita The legends surrounding El Dorado changed over time as it went from being a man to a city to a kingdom and then finally to an empire 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 95 From the late 15th to early 19th centuries European trade in the region was primarily focused in gold along with ivory and slaves 96 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 97 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 98 Gold played a role in western culture as a cause for desire and of corruption as told in children s fables such as Rumpelstiltskin where Rumpelstiltskin turns hay into gold for the peasant s daughter in return for her child when she becomes a princess and the stealing of the hen that lays golden eggs in Jack and the Beanstalk The top prize at the Olympic Games and many other sports competitions is the gold medal 75 of the presently accounted for gold has been extracted since 1910 two thirds since 1950 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 99 Their symbol for gold was the circle with a point at its center which was also the astrological symbol and the ancient Chinese character for the Sun The Dome of the Rock is covered with an ultra thin golden glassier The Sikh Golden temple the Harmandir Sahib is a building covered with gold Similarly the Wat Phra Kaew emerald Buddhist temple wat in Thailand has ornamental gold leafed statues and roofs Some European king and queen s crowns were made of gold and gold was used for the bridal crown since antiquity An ancient Talmudic text circa 100 AD describes Rachel wife of Rabbi Akiva receiving a Jerusalem of Gold diadem A Greek burial crown made of gold was found in a grave circa 370 BC Minoan jewellery 2300 2100 BC various sizes Metropolitan Museum of Art New York City Pair of Sumerian earrings with cuneiform inscriptions 2093 2046 BC Sulaymaniyah Museum Sulaymaniyah Iraq Ancient Egyptian statuette of Amun 945 715 BC gold 175 mm 47 mm 6 9 in 1 9 in Metropolitan Museum of Art Ancient Egyptian signet ring 664 525 BC gold diameter 30 mm 34 mm 1 2 in 1 3 in British Museum London Ancient Greek stater 323 315 BC 18 mm 0 71 in Metropolitan Museum of Art Etruscan funerary wreath 4th 3rd century BC length 333 mm 13 1 in Metropolitan Museum of Art Roman aureus of Hadrian 134 138 AD 7 4 g Metropolitan Museum of Art Quimbaya lime container 5th 9th century gold height 230 mm 9 1 in Metropolitan Museum of Art Byzantine scyphate 1059 1067 diameter 25 mm 0 98 in Cleveland Museum of Art Cleveland Ohio USA Pre Columbian pendant with two bat head warriors who carry spears 11th 16th century gold overall 76 2 mm 3 00 in from the Chiriqui Province Panama Metropolitan Museum of Art English Neoclassical box 1741 overall 44 mm 116 mm 92 mm 1 7 in 4 6 in 3 6 in Metropolitan Museum of Art French Rococo glass bottle mounted in gold circa 1775 overall 70 mm 29 mm 2 8 in 1 1 in Cleveland Museum of ArtEtymology An early mention of gold in the Beowulf Gold is cognate with similar words in many Germanic languages deriving via Proto Germanic gultha from Proto Indo European ǵʰelh to shine to gleam to be yellow or green 100 101 The symbol Au is from the Latin aurum the Latin word for gold 102 The Proto Indo European ancestor of aurum was h e h us o meaning glow This word is derived from the same root Proto Indo European h u es to dawn as h eu sōs the ancestor of the Latin word Aurora dawn 103 This etymological relationship is presumably behind the frequent claim in scientific publications that aurum meant shining dawn 104 Culture Gold crafts from the Philippines prior to Western contact In popular culture gold is a high standard of excellence often used in awards 44 Great achievements are frequently rewarded with gold in the form of gold medals gold trophies and other decorations Winners of athletic events and other graded competitions are usually awarded a gold medal Many awards such as the Nobel Prize are made from gold as well Other award statues and prizes are depicted in gold or are gold plated such as the Academy Awards the Golden Globe Awards the Emmy Awards the Palme d Or and the British Academy Film Awards 105 Aristotle in his ethics used gold symbolism when referring to what is now known as the golden mean Similarly gold is associated with perfect or divine principles such as in the case of the golden ratio and the golden rule Gold is further associated with the wisdom of aging and fruition The fiftieth wedding anniversary is golden A person s most valued or most successful latter years are sometimes considered golden years The height of a civilization is referred to as a golden age 106 Religion The Agusan image depicting a deity from northeast Mindanao In some forms of Christianity and Judaism gold has been associated both with the sacred and evil In the Book of Exodus the Golden Calf is a symbol of idolatry while in the Book of Genesis Abraham was said to be rich in gold and silver and Moses was instructed to cover the Mercy Seat of the Ark of the Covenant with pure gold In Byzantine iconography the halos of Christ Virgin Mary and the saints are often golden 107 In Islam 108 gold along with silk 109 110 is often cited as being forbidden for men to wear 111 Abu Bakr al Jazaeri quoting a hadith said that t he wearing of silk and gold are forbidden on the males of my nation and they are lawful to their women 112 This however has not been enforced consistently throughout history e g in the Ottoman Empire 113 Further small gold accents on clothing such as in embroidery may be permitted 114 In ancient Greek religion and mythology Theia was seen as the goddess of gold silver and other gems 115 According to Christopher Columbus those who had something of gold were in possession of something of great value on Earth and a substance to even help souls to paradise 116 Wedding rings are typically made of gold It is long lasting and unaffected by the passage of time and may aid in the ring symbolism of eternal vows before God and the perfection the marriage signifies In Orthodox Christian wedding ceremonies the wedded couple is adorned with a golden crown though some opt for wreaths instead during the ceremony an amalgamation of symbolic rites On 24 August 2020 Israeli archaeologists discovered a trove of early Islamic gold coins near the central city of Yavne Analysis of the extremely rare collection of 425 gold coins indicated that they were from the late 9th century Dating to around 1 100 years back the gold coins were from the Abbasid Caliphate 117 ProductionMain article List of countries by gold production Time trend of gold production According to the United 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 118 Mining and prospecting Main articles Gold mining and Gold prospecting A miner underground at Pumsaint gold mine Wales c 1938 Grasberg mine Indonesia is the world s largest gold mine Since the 1880s South Africa has been the source of a large proportion of the world s gold supply and about 22 of the gold presently accounted is from South Africa Production in 1970 accounted for 79 of the world supply about 1 480 tonnes In 2007 China with 276 tonnes overtook South Africa as the world s largest gold producer the first time since 1905 that South Africa had not been the largest 119 In 2020 China was the world s leading gold mining country followed in order by Russia Australia the United States Canada and Ghana 8 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 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 120 121 122 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 5 7 km 3 1 4 3 mi thick layer of archean rocks located in most places deep under the Free State Gauteng and surrounding provinces 123 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 63 123 From these surface exposures the basin dips extensively requiring some of the mining to occur at depths of nearly 4 000 m 13 000 ft 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 123 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 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 124 The first major gold strike in the United States occurred in a small north Georgia town called Dahlonega 125 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 126 Extraction and refining Main article Gold extraction Gold Nuggets found in Arizona Gold extraction is most economical in large easily mined deposits Ore grades as little as 0 5 parts per million ppm can be economical Typical ore grades in open pit mines are 1 5 ppm ore grades in underground or hard rock mines are usually at least 3 ppm Because ore grades of 30 ppm are usually needed before gold is visible to the naked eye in most gold mines the gold is invisible The average gold mining and extraction costs were about 317 per troy ounce in 2007 but these can vary widely depending on mining type and ore quality global mine production amounted to 2 471 1 tonnes 127 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 128 129 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 130 As of 2020 the amount of carbon dioxide CO2 produced in mining a kilogram of gold is 16 tonnes while recycling a kilogram of gold produces 53 kilograms of CO2 equivalent Approximately 30 percent of the global gold supply is recycled and not mined as of 2020 131 Corporations are starting to adopt gold recycling including jewelry companies such as Generation Collection and computer companies including Dell 132 Consumption This article needs to be updated Please help update this article to reflect recent events or newly available information May 2022 Gold jewelry consumption by country in tonnes 133 134 135 Country 2009 2010 2011 2012 2013 India 442 37 745 70 986 3 864 974 China 376 96 428 00 921 5 817 5 1120 1 United States 150 28 128 61 199 5 161 190 Turkey 75 16 74 07 143 118 175 2 Saudi Arabia 77 75 72 95 69 1 58 5 72 2 Russia 60 12 67 50 76 7 81 9 73 3 United Arab Emirates 67 60 63 37 60 9 58 1 77 1 Egypt 56 68 53 43 36 47 8 57 3 Indonesia 41 00 32 75 55 52 3 68 United Kingdom 31 75 27 35 22 6 21 1 23 4Other Persian Gulf Countries 24 10 21 97 22 19 9 24 6 Japan 21 85 18 50 30 1 7 6 21 3 South Korea 18 83 15 87 15 5 12 1 17 5 Vietnam 15 08 14 36 100 8 77 92 2 Thailand 7 33 6 28 107 4 80 9 140 1Total 1466 86 1770 71 2786 12 2477 7 3126 1Other Countries 251 6 254 0 390 4 393 5 450 7World Total 1718 46 2024 71 3176 52 2871 2 3576 8The consumption of gold produced in the world is about 50 in jewelry 40 in investments and 10 in industry 10 136 According to the World Gold Council China was the world s largest single consumer of gold in 2013 overtaking India 137 Pollution Further information Mercury cycle and International Cyanide Management Code Gold production is associated with contribution to hazardous pollution 138 139 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 140 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 141 142 Up to thirty tons of used ore can dumped as waste for producing one troy ounce of gold 143 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 are long term highly hazardous wastes second only to nuclear waste dumps 143 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 144 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 causes incurable brain function damage and severe retardation 145 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 146 Monetary useFurther information History of money 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 147 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 89 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 148 From an earlier preference in using silver European economies re established the minting of gold as coinage during the thirteenth and fourteenth centuries 149 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 150 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 151 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 152 for hardness American gold coins for circulation after 1837 contain an alloy of 0 900 fine gold or 21 6 kt 153 Although the prices of some platinum group metals can be much higher gold has long been considered the most desirable of precious metals and its value has been used as the standard for many currencies Gold has been used as a symbol for purity value royalty and particularly roles that combine these properties Gold as a sign of wealth and prestige was ridiculed by Thomas More in his treatise Utopia On that imaginary island gold is so abundant that it is used to make chains for slaves tableware and lavatory seats When ambassadors from other countries arrive dressed in ostentatious gold jewels and badges the Utopians mistake them for menial servants paying homage instead to the most modestly dressed of their party The ISO 4217 currency code of gold is XAU 154 Many holders of gold store it in form of bullion coins or bars as a hedge against inflation or other economic disruptions though its efficacy as such has been questioned historically it has not proven itself reliable as a hedging instrument 155 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 92 156 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 157 Price Further information Gold as an investment Gold price history in 1960 2020 As of September 2017 update gold is valued at around 42 per gram 1 300 per troy ounce 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 158 History Historically gold coinage was widely used as currency when paper money was introduced it typically was a receipt redeemable for gold coin or bullion In a monetary system known as the gold standard a certain weight of gold was given the name of a unit of currency For a long period the United States government set the value of the US dollar so that one troy ounce was equal to 20 67 0 665 per gram but in 1934 the dollar was devalued to 35 00 per troy ounce 0 889 g By 1961 it was becoming hard to maintain this price and a pool of US and European banks agreed to manipulate the market to prevent further currency devaluation against increased gold demand 159 On 17 March 1968 economic circumstances clarification needed caused the collapse of the gold pool and a two tiered pricing scheme was established whereby gold was still used to settle international accounts at the old 35 00 per troy ounce 1 13 g but the price of gold on the private market was allowed to fluctuate this two tiered pricing system was abandoned in 1975 when the price of gold was left to find its free market level citation needed Central banks still hold historical gold reserves as a store of value although the level has generally been declining citation needed The largest gold depository in the world is that of the U S Federal Reserve Bank in New York which holds about 3 160 of the gold known to exist and accounted for today as does the similarly laden U S Bullion Depository at Fort Knox In 2005 the World Gold Council estimated total global gold supply to be 3 859 tonnes and demand to be 3 754 tonnes giving a surplus of 105 tonnes 161 After 15 August 1971 Nixon shock the price began to greatly increase 162 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 163 Prices increased rapidly from 2001 but the 1980 high was not exceeded until 3 January 2008 when a new maximum of 865 35 per troy ounce was set 164 Another record price was set on 17 March 2008 at 1023 50 per troy ounce 32 91 g 164 In late 2009 gold markets experienced renewed momentum upwards due to increased demand and a weakening US dollar citation needed On 2 December 2009 gold reached a new high closing at 1 217 23 165 Gold further rallied hitting new highs in May 2010 after the European Union debt crisis prompted further purchase of gold as a safe asset 166 167 On 1 March 2011 gold hit a new all time high of 1432 57 based on investor concerns regarding ongoing unrest in North Africa as well as in the Middle East 168 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 169 prompting speculation that the long secular bear market had ended and a bull market had returned 170 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 complexive growth of 59 from August 2018 to October 2020 a period during which it outplaced the Nasdaq total return of 54 171 Gold futures are traded on the COMEX exchange 172 These contacts are priced in USD per troy ounce 1 troy ounce 31 1034768 grams 173 Below are the CQG contract specifications outlining the futures contracts Contract Specifications 172 Gold GCA Exchange COMEXSector MetalTick Size 0 1Tick Value 10 USDBPV 100Denomination USDDecimal Place 1Medicinal uses Medicinal applications of gold and its complexes have a long history dating back thousands of years 174 Several gold complexes have been applied to treat rheumatoid arthritis the most frequently used being aurothiomalate aurothioglucose and auranofin Both gold I and gold III compounds have been investigated as possible anti cancer drugs For gold III complexes reduction to gold 0 I under physiological conditions has to be considered Stable complexes can be generated using different types of bi tri and tetradentate ligand systems and their efficacy has been demonstrated in vitro and in vivo 175 Other applicationsJewelry Moche gold necklace depicting feline heads Larco Museum Collection Lima Peru A 21 5k yellow gold pendant watch so called Boule de Geneve Geneva ball ca 1890 Because of the softness of pure 24k gold it is usually alloyed with base 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 or other base metals or silver or palladium in the alloy 24 Nickel is toxic and its release from nickel white gold is controlled by legislation in Europe 24 Palladium gold alloys are more expensive than those using nickel 176 High karat white gold alloys are more resistant to corrosion than are either pure silver or sterling silver The Japanese craft of Mokume gane exploits the color contrasts between laminated colored gold alloys to produce decorative wood grain effects By 2014 the gold jewelry industry was escalating despite a dip in gold prices Demand in the first quarter of 2014 pushed turnover to 23 7 billion according to a World Gold Council report Gold solder is used for joining the components of gold jewelry by high temperature hard soldering or brazing If the work is to be of hallmarking quality the gold solder alloy must match the fineness purity 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 10 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 2 dollars 82 cents 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 177 Prices updated to November 2022 Though gold is attacked by free chlorine its good conductivity and general resistance to oxidation and corrosion in other environments including resistance to non chlorinated acids has led to its widespread industrial use in the electronic era as a thin layer coating on electrical connectors thereby ensuring good connection For example gold is used in the connectors of the more expensive electronics cables such as audio video and USB cables The benefit of using gold over other connector metals such as tin in these applications has been debated gold connectors are often criticized by audio visual experts as unnecessary for most consumers and seen as simply a marketing ploy However the use of gold in other applications in electronic sliding contacts in highly humid or corrosive atmospheres and in use for contacts with a very high failure cost certain computers communications equipment spacecraft jet aircraft engines remains very common 178 Besides sliding electrical contacts gold is also used in electrical contacts because of its resistance to corrosion electrical conductivity ductility and lack of toxicity 179 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 3 180 Gold is highly conductive to electricity and has been used for electrical wiring in some high energy applications only silver and copper are more conductive per volume but gold has the advantage of corrosion resistance For example gold electrical wires were used during some of the Manhattan Project s atomic experiments but large high current silver wires were used in the calutron isotope separator magnets in the project It is estimated that 16 of the world s presently accounted for gold and 22 of the world s silver is contained in electronic technology in Japan 181 Medicine 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 182 and known to Dioscorides 183 184 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 Even some modern esotericists and forms of alternative medicine assign metallic gold a healing power 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 185 The apparent paradox of the actual toxicology of the substance suggests the possibility of serious gaps in the understanding of the action of gold in physiology 186 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 Some gold salts do have anti inflammatory properties and at present two are still used as pharmaceuticals in the treatment of arthritis and other similar conditions in the US sodium aurothiomalate and auranofin 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 187 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 188 In ultrathin sections of tissues viewed by electron microscopy the immunogold labels appear as extremely dense round spots at the position of the antigen 189 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 190 The isotope gold 198 half life 2 7 days is used in nuclear medicine in some cancer treatments and for treating other diseases 191 192 Cuisine Cake with gold decoration served at the Amstel Hotel Amsterdam Gold can be used in food and has the E number 175 193 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 194 Gold leaf flake or dust is used on and in some gourmet foods notably sweets and drinks as decorative ingredient 195 Gold flake was used by the nobility in medieval Europe as a decoration in food and drinks 196 in the form of leaf flakes or dust either to demonstrate the host s wealth or in the belief that something that valuable and rare must be beneficial for one s health citation needed Danziger Goldwasser German Gold water of Danzig or Goldwasser English Goldwater is a traditional German herbal liqueur 197 produced in what is today Gdansk Poland and Schwabach Germany and contains flakes of gold leaf There are also some expensive c 1000 cocktails which contain flakes of gold leaf However since metallic gold is inert to all body chemistry it has no taste it provides no nutrition and it leaves the body unaltered 198 Vark is a foil composed of a pure metal that is sometimes gold 199 and is used for garnishing sweets in South Asian cuisine Miscellanea Mirror for the James Webb Space Telescope coated in gold to reflect infrared light Kamakshi Amman Temple with golden roof Kanchipuram Gold produces a deep intense red color when used as a coloring agent in cranberry glass In photography gold toners are used to shift the color of silver bromide black and white prints towards brown or blue tones or to increase their stability Used on sepia toned prints gold toners produce red tones Kodak published formulas for several types of gold toners which use gold as the chloride 200 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 201 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 202 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 203 Gold when dispersed in nanoparticles can act as a heterogeneous catalyst of chemical reactions ToxicityPure metallic elemental gold is non toxic and non irritating when ingested 204 and is sometimes used as a food decoration in the form of gold leaf 205 Metallic gold is also a component of the alcoholic drinks Goldschlager 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 206 207 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 208 Despite this gold is a relatively non potent contact allergen in comparison with metals like nickel 209 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 210 See also Iron pyrite or fool s gold Bulk leach extractable gold for sampling ores Chrysiasis dermatological condition Digital gold currency form of electronic currency GFMS business consultancy Gold fingerprinting use impurities to identify an alloy Gold standard in banking List of countries by gold production Tumbaga alloy of gold and copper Iron pyrite fool s gold Nordic gold non gold copper alloyReferences Standard Atomic Weights Gold CIAAW 2017 Mezaille Nicolas Avarvari Narcis Maigrot Nicole Ricard Louis Mathey Francois Le Floch Pascal Cataldo Laurent Berclaz Theo Geoffroy Michel 1999 Gold I and Gold 0 Complexes of Phosphinine Based Macrocycles Angewandte Chemie International Edition 38 21 3194 3197 doi 10 1002 SICI 1521 3773 19991102 38 21 lt 3194 AID ANIE3194 gt 3 0 CO 2 O PMID 10556900 Lide D R ed 2005 Magnetic susceptibility of the elements and inorganic compounds CRC Handbook of Chemistry and Physics PDF 86th ed Boca Raton FL CRC Press ISBN 0 8493 0486 5 Weast Robert 1984 CRC Handbook of Chemistry and Physics Boca Raton Florida Chemical Rubber Company Publishing pp E110 ISBN 0 8493 0464 4 Kelly P F 2015 Properties of Materials CRC Press p 355 ISBN 978 1 4822 0624 1 Duckenfield Mark 2016 The Monetary History of Gold A Documentary History 1660 1999 Routledge p 4 ISBN 9781315476124 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 Pearce Susan M 1993 Museums Objects and Collections A Cultural Study Smithsonian Books p 53 ISBN 9781588345172 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 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Journal 14 1 4362 2016 doi 10 2903 j efsa 2016 4362 ISSN 1831 4732 The Food Dictionary Varak Barron s Educational Services Inc 1995 Archived from the original on 23 May 2006 Retrieved 27 May 2007 Kerner Susanne Chou Cynthia Warmind Morten 2015 Commensality From Everyday Food to Feast Bloomsbury Publishing p 94 ISBN 978 0 85785 719 4 Baedeker Karl 1865 Danzig Deutschland nebst Theilen der angrenzenden Lander in German Karl Baedeker King Hobart M The Many Uses of Gold geology com Retrieved 6 June 2009 Gold in Gastronomy Archived 4 March 2016 at the Wayback Machine deLafee Switzerland 2008 Toning black and white materials Kodak Technical Data Reference sheet G 23 May 2006 Martin Keith 1997 McLaren F1 The Demand for Gold by Industry PDF Gold bulletin Archived from the original PDF on 26 July 2011 Retrieved 6 June 2009 Colored glass chemistry Archived from the original on 13 February 2009 Retrieved 6 June 2009 Dierks S May 2005 Gold MSDS Electronic Space Products International Archived from the original on 10 November 2006 Retrieved 21 December 2021 Louis Catherine Pluchery Olivier 2012 Gold Nanoparticles for Physics Chemistry and Biology World Scientific ISBN 978 1 84816 807 7 Wright I H Vesey J C 1986 Acute poisoning with gold cyanide Anaesthesia 41 79 936 939 doi 10 1111 j 1365 2044 1986 tb12920 x PMID 3022615 S2CID 32434351 Wu Ming Ling Tsai Wei Jen Ger Jiin Deng Jou Fang Tsay Shyh Haw et al 2001 Cholestatic Hepatitis Caused by Acute Gold Potassium Cyanide Poisoning Clinical Toxicology 39 7 739 743 doi 10 1081 CLT 100108516 PMID 11778673 S2CID 44722156 Tsuruta Kyoko Matsunaga Kayoko Suzuki Kayoko Suzuki Rie Akita Hirotaka Washimi Yasuko Tomitaka Akiko Ueda Hiroshi 2001 Female predominance of gold allergy Contact Dermatitis 44 1 48 49 doi 10 1034 j 1600 0536 2001 440107 22 x PMID 11156030 S2CID 42268840 Brunk Doug 15 February 2008 Ubiquitous nickel wins skin contact allergy award for 2008 Archived from the original on 24 June 2011 Singh Harbhajan 2006 Mycoremediation Fungal Bioremediation p 509 ISBN 978 0 470 05058 3 Further readingBachmann H G The lure of gold an artistic and cultural history 2006 online Bernstein Peter L The Power of Gold The History of an Obsession 2000 online Brands H W The Age of Gold The California Gold Rush and the New American Dream 2003 excerpt Buranelli Vincent Gold an illustrated history 1979 online wide ranging popular history Cassel Gustav The restoration of the gold standard Economica 9 1923 171 185 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 online Hart Matthew Gold The Race for the World s Most Seductive Metal Gold the race for the world s most seductive metal New York Simon amp Schuster 2013 ISBN 9781451650020 Johnson Harry G The gold rush of 1968 in retrospect and prospect American Economic Review 59 2 1969 344 348 online Kwarteng Kwasi War and Gold A Five Hundred Year History of Empires Adventures and Debt 2014 online Vilar Pierre A History of Gold and Money 1450 1920 1960 online Vilches Elvira New World Gold Cultural Anxiety and Monetary Disorder in Early Modern Spain 2010 External links Wikiquote has quotations related to Gold Wikimedia Commons has media related to Gold Look up gold in Wiktionary the free dictionary Gold Encyclopaedia Britannica Vol 11 11th ed 1911 Chemistry in its element podcast MP3 from the Royal Society of Chemistry s Chemistry World Gold www rsc org Gold at The Periodic Table of Videos University of Nottingham Getting Gold 1898 book www lateralscience co uk Technical Document on Extraction and Mining of Gold at the Wayback Machine archived 7 March 2008 www epa gov Gold element information rsc org Retrieved from https en wikipedia org w index php title Gold amp oldid 1133307529, wikipedia, wiki, book, books, library,

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