======================================================================
= Gold =
======================================================================
Introduction
======================================================================
Gold is a chemical element; it has chemical symbol Au (from Latin )
and atomic number 79. In its pure form, it is a bright, slightly
orange-yellow, dense, soft, malleable, and ductile metal. Chemically,
gold is a transition metal, a group 11 element, and one of the noble
metals. It is one of the least reactive chemical elements, being the
second-lowest in the reactivity series. It is solid under standard
conditions.
Gold often occurs in free elemental (native state), as nuggets or
grains, in rocks, veins, and alluvial deposits. It occurs in a solid
solution series with the native element silver (as in electrum),
naturally alloyed with other metals like copper and palladium, and
mineral inclusions such as within pyrite. Less commonly, it occurs in
minerals as gold compounds, often with tellurium (gold tellurides).
Gold is resistant to most acids, though it does dissolve in aqua regia
(a mixture of nitric acid and hydrochloric acid), forming a soluble
tetrachloroaurate anion. Gold is insoluble in nitric acid alone, which
dissolves silver and base metals, a property long used to refine gold
and confirm the presence of gold in metallic substances, giving rise
to the term "acid test". Gold dissolves in alkaline solutions of
cyanide, which are used in mining and electroplating. Gold also
dissolves in mercury, forming amalgam alloys, and as the gold acts
simply as a solute, this is not a chemical reaction.
A relatively rare element, gold is a precious metal that has been used
for coinage, jewelry, and other works of art throughout recorded
history. In the past, a gold standard was often implemented as a
monetary policy. Gold coins ceased to be minted as a circulating
currency in the 1930s, and the world gold standard was abandoned for a
fiat currency system after the Nixon shock measures of 1971.
In 2023, the world's largest gold producer was China, followed by
Russia and Australia. , a total of around 201,296 tonnes of gold exist
above ground. If all of this gold were put together into a cube shape,
each of its sides would measure 21.7 m. The world's consumption of new
gold produced is about 50% in jewelry, 40% in investments, and 10% in
industry. Gold's high malleability, ductility, resistance to corrosion
and most other chemical reactions, as well as conductivity of
electricity have led to its continued use in corrosion-resistant
electrical connectors in all types of computerized devices (its chief
industrial use). Gold is also used in infrared shielding, the
production of colored glass, gold leafing, and tooth restoration.
Certain gold salts are still used as anti-inflammatory agents in
medicine.
Characteristics
======================================================================
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. Such nanowires distort via the formation, reorientation, and
migration of dislocations and crystal twins without noticeable
hardening. A single gram of gold can be beaten into a sheet of 1 m2,
and an avoirdupois ounce into 300 sqft. Gold leaf can be beaten thin
enough to become semi-transparent. The transmitted light appears
greenish-blue because gold strongly reflects yellow and red. Such
semi-transparent sheets also strongly reflect infrared light, making
them useful as infrared (radiant heat) shields in the visors of
heat-resistant suits and in sun visors for spacesuits. Gold is a good
conductor of heat and electricity.
Gold has a density of 19.3 g/cm3, almost identical to that of tungsten
at 19.25 g/cm3; as such, tungsten has been used in the counterfeiting
of gold bars, such as by plating a tungsten bar with gold. By
comparison, the density of lead is 11.34 g/cm3, and that of the
densest element, osmium, is .
Color
=======
Whereas most metals are gray or silvery white, gold is slightly
reddish-yellow. 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. 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.
Colloidal gold, used by electron-microscopists, is red if the
particles are small; larger particles of colloidal gold are blue.
Isotopes
==========
Gold has only one stable isotope, , 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 with a
half-life of 186.1 days. The least stable is , 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 , which decays by electron
capture, and , which decays most often by electron capture (93%) with
a minor β− decay path (7%). All of gold's radioisotopes with atomic
masses above 197 decay by β− decay.
At least 32 nuclear isomers have also been characterized, ranging in
atomic mass from 170 to 200. Within that range, only , , , , and do
not have isomers. Gold's most stable isomer is with a half-life of
2.27 days. Gold's least stable isomer is with a half-life of only 7
ns. has three decay paths: β+ decay, isomeric transition, and alpha
decay. No other isomer or isotope of gold has three decay paths.
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. 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.
In 1980, Glenn Seaborg transmuted several thousand atoms of bismuth
into gold at the Lawrence Berkeley Laboratory. 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.
Chemistry
======================================================================
Although gold is the most noble of the noble metals, 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 , 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.
Au(III) (referred to as auric) is a common oxidation state, and is
illustrated by gold(III) chloride, . 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 and, up to 100 °C,
is resistant to attack from ozone:
Some free halogens react to form the corresponding gold halides. Gold
is strongly attacked by fluorine at dull-red heat to form gold(III)
fluoride . Powdered gold reacts with chlorine at 180 °C to form
gold(III) chloride . Gold reacts with bromine at 140 °C to form a
combination of gold(III) bromide and gold(I) bromide AuBr, but reacts
very slowly with iodine to form gold(I) iodide AuI:
2 Au{} + 3 F2 ->[{}\atop\Delta] 2 AuF3
2 Au{} + 3 Cl2 ->[{}\atop\Delta] 2 AuCl3
2 Au{} + 2 Br2 ->[{}\atop\Delta] AuBr3{} + AuBr
2 Au{} + I2 ->[{}\atop\Delta] 2 AuI
Gold does not react with sulfur directly, but gold(III) sulfide can be
made by passing hydrogen sulfide through a dilute solution of
gold(III) chloride or chlorauric acid.
Unlike sulfur, phosphorus reacts directly with gold at elevated
temperatures to produce gold phosphide (Au2P3).
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.
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 ions, or chloroauric acid, thereby enabling further
oxidation:
2 Au{} + 6 H2SeO4 ->[{}\atop{200^\circ\text{C}}] Au2(SeO4)3{} + 3
H2SeO3{} + 3 H2O
Au{} + 4HCl{} + HNO3 -> HAuCl4{} + 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.
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
anion. Caesium auride (CsAu), for example, crystallizes in the caesium
chloride motif; rubidium, potassium, and tetramethylammonium aurides
are also known. Gold has the highest electron affinity of any metal,
at 222.8 kJ/mol, making a stable species, 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.
Gold(II) compounds are usually diamagnetic with Au-Au bonds such as [.
The evaporation of a solution of in concentrated produces red
crystals of gold(II) sulfate, . Originally thought to be a
mixed-valence compound, it has been shown to contain cations,
analogous to the better-known mercury(I) ion, . A gold(II) complex,
the tetraxenonogold(II) cation, which contains xenon as a ligand,
occurs in . In September 2023, a novel type of metal-halide perovskite
material consisting of Au3+ and Au2+ cations in its crystal structure
has been found. It has been shown to be unexpectedly stable at normal
conditions.
Gold pentafluoride, along with its derivative anion, , and its
difluorine complex, gold heptafluoride, is the sole example of
gold(V), the highest verified oxidation state.
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. In some cases, gold has a
fractional oxidation state. A representative example is the octahedral
species {{chem2|{Au(P(C6H5)3)}6(2+)}}.
Gold production in the universe
=================================
Gold in the universe is produced through several cosmic processes and
was present in the dust from which the Solar System formed. Scientists
have identified three main cosmic sources for gold formation:
supernova nucleosynthesis, neutron star collisions, and magnetar
flares.
All three sources involve a process called the r-process (rapid
neutron capture), which forms elements heavier than iron. For decades,
scientists believed supernova nucleosynthesis was the primary
mechanism for gold formation. More recently, research has shown that
neutron star collisions produce significant quantities of gold through
the r-process.
In August 2017, the spectroscopic signatures of heavy elements,
including gold, were directly observed by electromagnetic
observatories during the GW170817 neutron star merger event. This
confirmed neutron star mergers as a source of gold, after years of
only indirect detection. This single event generated between 3 and 13
Earth masses of gold, suggesting that neutron star mergers might
produce enough gold to account for most of this element in the
universe.
However, neutron star mergers alone cannot explain all cosmic gold,
particularly in older stars, because these mergers occur relatively
late in galactic history and are infrequent (approximately once every
100,000 years). This created a timing paradox in explaining the
presence of gold in stars formed early in the universe.
In 2025, researchers resolved this paradox by confirming that giant
flares from magnetars (highly magnetic neutron stars) are also a
significant source of gold formation. Analysis of a 2004 magnetar
flare showed these events produce heavy elements through the same
r-process as neutron star mergers. The amount of heavy elements
created in a single magnetar flare can exceed the mass of Mars. Since
magnetars existed earlier in cosmic history and flare more frequently
than neutron star mergers occur, they help explain gold's presence in
older stars. Scientists estimate magnetar flares may contribute
approximately 1-10% of all elements heavier than iron in our galaxy,
including gold.
Asteroid origin theories
==========================
Because the Earth was molten when it was formed, almost all of the
gold present in the early Earth probably sank into the planetary core.
Therefore, as hypothesized in one model, most of the gold in the
Earth's crust and mantle is thought to have been delivered to Earth by
asteroid impacts during the Late Heavy Bombardment, about 4 billion
years ago.
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. However, this scenario is now questioned. The
gold-bearing Witwatersrand rocks were laid down between 700 and 950
million years before the Vredefort impact. 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 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.
Mantle return theories
========================
Much of the rest of the gold on Earth is thought to have been
incorporated into the planet since its very beginning, as
planetesimals formed the mantle. In 2017, an international group of
scientists established that gold "came to the Earth's surface from the
deepest regions of our planet", the mantle, as evidenced by their
findings at Deseado Massif in the Argentinian Patagonia.
Occurrence
======================================================================
On Earth, gold is found in ores in rock formed from the Precambrian
time onward. 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. These are called lode deposits. The metal in
a native state is also found in the form of free flakes, grains or
larger nuggets 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 () and
antimonide aurostibite (). Gold also occurs in rare alloys with
copper, lead, and mercury: the minerals auricupride (), novodneprite
() and weishanite ().
A 2004 research paper suggests that microbes can sometimes play an
important role in forming gold deposits, transporting and
precipitating gold to form grains and nuggets that collect in alluvial
deposits.
A 2013 study has claimed water in faults vaporizes during an
earthquake, depositing gold. When an earthquake strikes, it moves
along a fault. Water often lubricates faults, filling in fractures and
jogs. About 10 km below the surface, under very high temperatures and
pressures, the water carries high concentrations of carbon dioxide,
silica, and gold. During an earthquake, the fault jog suddenly opens
wider. The water inside the void instantly vaporizes, flashing to
steam and forcing silica, which forms the mineral quartz, and gold out
of the fluids and onto nearby surfaces.
Seawater
==========
The world's oceans contain gold. Measured concentrations of gold in
the Atlantic and Northeast Pacific are 50-150 femtomol/L or 10-30
parts per quadrillion (about 10-30 g/km3). In general, gold
concentrations for south Atlantic and central Pacific samples are the
same (~50 femtomol/L) but less certain. Mediterranean deep waters
contain slightly higher concentrations of gold (100-150 femtomol/L),
which is attributed to wind-blown dust or rivers. At 10 parts per
quadrillion, the Earth's oceans would hold 15,000 tonnes of gold.
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. 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. 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.
History
======================================================================
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, .
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.
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. 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. 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. Egyptian
hieroglyphs from as early as 2600 BC describe gold, which King
Tushratta of the Mitanni claimed was "more plentiful than dirt" in
Egypt. 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.
Gold is mentioned in the Amarna letters numbered 19 and 26 from around
the 14th century BC.
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. 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. A contemporary Arab historian remarked:
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.
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.
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". From the late 15th to early 19th
centuries, European trade in the region was primarily focused in gold,
along with ivory and slaves. 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. 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.
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. 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.
Gold leaf MET DP260372.jpg|Minoan jewellery, 2300-2100 BC, gold,
Metropolitan Museum of Art, New York
Earrings from Shulgi.JPG|Sumerian earrings with cuneiform
inscriptions, 2093-2046 BC, gold, Sulaymaniyah Museum, Sulaymaniyah,
Iraq
File:Aegina treasure 10.jpg|Minoan cup, part of the Aegina Treasure,
1850-1550 BC, gold, British Museum
Statuette of Amun MET DT553.jpg|Ancient Egyptian statuette of Amun,
945-715 BC, gold, Metropolitan Museum of Art
Anillo de Sheshonq (46627183381).jpg|Ancient Egyptian signet ring,
664-525 BC, gold, British Museum
File:Openwork dagger handle-IMG 4418-black.jpg|Ancient Chinese cast
openwork dagger hilt, 6th-5th centuries BC, gold, British Museum
Gold stater MET DP138743.jpg|Ancient Greek stater, 323-315 BC, gold,
Metropolitan Museum of Art
Gold funerary wreath MET DP257471.jpg|Etruscan funerary wreath,
4th-3rd century BC, gold, Metropolitan Museum of Art
Gold aureus of Hadrian MET DP104782b.jpg|Roman aureus of Hadrian,
134-138 AD, gold, Metropolitan Museum of Art
Lime Container (Poporo) MET DT1262.jpg|Quimbaya lime container,
5th-9th century, gold, Metropolitan Museum of Art
File:British Museum - Room 41 (20626313758).jpg|Anglo-Saxon belt
buckle from Sutton Hoo with a niello interlace pattern, 7th century,
gold, British Museum
Byzantium, 11th century - Scyphate - 2001.25 - Cleveland Museum of
Art.tif|Byzantine scyphate, 1059-1067, gold, Cleveland Museum of Art,
Cleveland, Ohio, USA
Double Bat-Head Figure Pendant MET DT935.jpg|Pre-Columbian pendant
with two bat-head warriors who carry spears, 11th-16th century, gold,
Metropolitan Museum of Art
File:AHOTWgold lama.JPG|Inca hollow model of a llama, 14th-15th
centuries, gold, British Museum
File:The Judgement of Paris, Waddeson Bequest.jpg|Renaissance hat
badge that shows the Judgment of Paris, 16th century, enamelled gold,
British Museum
Box with scene depicting Roman hero Gaius Mucius Scaevola before the
Etruscan king Lars Porsena MET DP170836 (cropped).jpg|Rococo box, by
George Michael Moser, 1741, gold, Metropolitan Museum of Art
Jean Joseph de Saint-Germain - Candelabrum - 1946.81 - Cleveland
Museum of Art.tif|Rococo candelabrum, by Jean Joseph de Saint-Germain,
1750, gilt bronze, Cleveland Museum of Art
Tabatière Minerve, Mercure, Pégase (Louvre, OA 2121).jpg|Rococo snuff
box with Minerva, by Jean-Malquis Lequin, 1750-1752, gold and painted
enamel, Louvre
File:Tabatière J-Frémin (Louvre, OA 6857).jpg|Louis XVI style snuff
box, by Jean Frémin, 1763-1764, gold and painted enamel, Louvre
File:Washstand (athénienne or lavabo) MET DP106594.jpg|Neoclassical
washstand (athénienne or lavabo), 1800-1814, legs, base and shelf of
yew wood, gilt bronze mounts, iron plate beneath shelf, Metropolitan
Museum of Art
File:Clock, French, circa 1835-1840, gilt and patinated bronze,
inherited from Maurice Quentin Bauchart, 1911, inv. 17741, Museum of
Decorative Arts, Paris.jpg|Gothic Revival clock, unknown French maker,
1835-1840, gilt and patinated bronze, Museum of Decorative Arts, Paris
File:Teapot, by Alphonse Debain, from Paris, 1900, gilt silver and
ivory, inv. 2021.63.1 MAD Paris.jpg|Art Nouveau teapot, by Alphonse
Debain, gilt silver and ivory, Museum of Decorative Arts
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.
The largest gold depository in the world is that of the U.S. Federal
Reserve Bank in New York, which holds about 3% 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.
After 15 August 1971 Nixon shock, the price began to greatly increase,
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).
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. Another record price was set on 17 March 2008, at $1023.50 per
troy ounce ($32.91/g).
On 2 December 2009, gold reached a new high closing at $1,217.23. Gold
further rallied hitting new highs in May 2010 after the European Union
debt crisis prompted further purchase of gold as a safe asset. 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.
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, prompting speculation that the long
secular bear market had ended and a bull market had returned. However,
the price then began a slow decline towards $1200 per troy ounce in
late 2014 and 2015.
In August 2020, the gold price picked up to US$2060 per ounce after a
total growth of 59% from August 2018 to October 2020, a period during
which it outplaced the Nasdaq total return of 54%.
Gold futures are traded on the COMEX exchange. These contacts are
priced in USD per troy ounce (1 troy ounce = 31.1034768 grams). Below
are the CQG contract specifications outlining the futures contracts:
Contract Specifications
!Gold (GCA) !
|Exchange: |COMEX
|Sector: |Metal
|Tick Size: |0.1
|Tick Value: |10 USD
|BPV: |100
|Denomination: |USD
|Decimal Place: |1
Etymology
===========
'Gold' is cognate with similar words in many Germanic languages,
deriving via Proto-Germanic *'gulþą' from Proto-Indo-European
*'ǵʰelh₃-' .
The symbol 'Au' is from the Latin . The Proto-Indo-European ancestor
of 'aurum' was '*h₂é-h₂us-o-', meaning . This word is derived from the
same root (Proto-Indo-European '*h₂u̯es-' ) as '*h₂éu̯sōs', the
ancestor of the Latin word . This etymological relationship is
presumably behind the frequent claim in scientific publications that
meant .
Culture
=========
In popular culture gold is a high standard of excellence, often used
in awards. 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).
Aristotle in his ethics used gold symbolism when referring to what is
now known as the golden mean. Similarly, gold is associated with
perfect or divine principles, such as in the case of the golden ratio
and the Golden Rule. Gold is further associated with the wisdom of
aging and fruition. The fiftieth wedding anniversary is golden. A
person's most valued or most successful latter years are sometimes
considered "golden years" or "golden jubilee". The height of a
civilization is referred to as a golden age.
Religion
==========
The first known prehistoric human usages of gold were religious in
nature.
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.
In Islam, gold (along with silk) is often cited as being forbidden for
men to wear. 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". This, however, has not been enforced
consistently throughout history, e.g. in the Ottoman Empire. Further,
small gold accents on clothing, such as in embroidery, may be
permitted.
In ancient Greek religion and mythology, Theia was seen as the goddess
of gold, silver and other gemstones.
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.
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.
Production
======================================================================
According to the United States Geological Survey in 2016, about
5,726,000,000 ozt of gold has been accounted for, of which 85% remains
in active use.
Mining and prospecting
========================
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.
In 2023, China was the world's leading gold-mining country, followed
in order by Russia, Australia, Canada, the United States and Ghana.
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.
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 thick layer of archean rocks
located, in most places, deep under the Free State, Gauteng and
surrounding provinces. 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. From these surface exposures the
basin dips extensively, requiring some of the mining to occur at
depths of nearly , 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.
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.
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. The first major gold strike in the United States
occurred in a small north Georgia town called Dahlonega. 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.
Extraction and refining
=========================
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.
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. 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.
Recycling
===========
In 1997, recycled gold accounted for approximately 20% of the 2700
tons of gold supplied to the market. Jewelry companies such as
Generation Collection and computer companies including Dell conduct
recycling.
As of 2020, the amount of carbon dioxide produced in mining a
kilogram of gold is 16 tonnes, while recycling a kilogram of gold
produces 53 kilograms of equivalent. Approximately 30 percent of the
global gold supply is recycled and not mined as of 2020.
Consumption
=============
Gold jewelry consumption by country (in tonnes)
Country !! 2009 !! 2010 !! 2011 !! 2012 !! 2013
align=left| 442.37 745.70 986.3 864 974
align=left| 376.96 428.00 921.5 817.5 1120.1
align=left| 150.28 128.61 199.5 161 190
align=left| 75.16 74.07 143 118 175.2
align=left| 77.75 72.95 69.1 58.5 72.2
align=left| 60.12 67.50 76.7 81.9 73.3
align=left| 67.60 63.37 60.9 58.1 77.1
align=left| 56.68 53.43 36 47.8 57.3
align=left| 41.00 32.75 55 52.3 68
align=left| 31.75 27.35 22.6 21.1 23.4
align=left|Other Persian Gulf Countries 24.10 21.97 22 19.9
24.6
align=left| 21.85 18.50 −30.1 7.6 21.3
align=left| 18.83 15.87 15.5 12.1 17.5
align=left| 15.08 14.36 100.8 77 92.2
align=left| 7.33 6.28 107.4 80.9 140.1
| align=left|**Total** || **1466.86** || **1770.71** || **2786.12 **
|| **2477.7** || **3126.1 **
align=left|'Other Countries' '251.6' '254.0' '390.4' '393.5'
'450.7'
| align=left|**World Total** || **1718.46** || **2024.71** ||
**3176.52**|| **2871.2** || **3576.8**
The consumption of gold produced in the world is about 50% in jewelry,
40% in investments, and 10% in industry.
According to the World Gold Council, China was the world's largest
single consumer of gold in 2013, overtaking India.
Pollution
===========
Gold production is associated with contribution to hazardous
pollution.
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 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. Up to thirty tons
of used ore can be dumped as waste for producing one troy ounce of
gold. Gold ore dumps are the source of many heavy elements such as
cadmium, lead, zinc, copper, arsenic, selenium and mercury. When
sulfide-bearing minerals in these ore dumps are exposed to air and
water, the sulfide transforms into sulfuric acid which in turn
dissolves these heavy metals facilitating their passage into surface
water and ground water. This process is called acid mine drainage.
These gold ore dumps contain long-term, highly hazardous waste.
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. Minute quantities of mercury compounds can reach water bodies,
causing heavy metal contamination. Mercury can then enter into the
human food chain in the form of methylmercury. Mercury poisoning in
humans can cause severe brain damage.
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.
Monetary use
======================================================================
Gold has been widely used throughout the world as money, 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. 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. From an earlier
preference in using silver, European economies re-established the
minting of gold as coinage during the thirteenth and fourteenth
centuries.
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.
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. 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,
for hardness (American gold coins for circulation after 1837 contain
an alloy of 0.900 fine gold, or 21.6 kt).
Often the prices of various platinum group metals can be much higher
than gold. Though gold has been used as a standard for currencies to a
greater degree than the platinum group metals. Gold has been used as a
symbol for purity, value, royalty, and particularly roles that combine
these properties. Gold as a sign of wealth and prestige was ridiculed
by Thomas More in his treatise 'Utopia'. On that imaginary island,
gold is so abundant that it is used to make chains for slaves,
tableware, and lavatory seats. When ambassadors from other countries
arrive, dressed in ostentatious gold jewels and badges, the Utopians
mistake them for menial servants, paying homage instead to the most
modestly dressed of their party.
The ISO 4217 currency code of gold is XAU. 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. 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).
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.
Price
=======
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. , gold was valued at around
$106 per gram ($3,300 per troy ounce).
Jewelry
=========
Because of the softness of pure (24k) gold, it is usually alloyed with
other metals for use in jewelry, altering its hardness and ductility,
melting point, color and other properties. Alloys with lower karat
rating, typically 22k, 18k, 14k or 10k, contain higher percentages of
copper, silver, palladium or other base metals in the alloy. Nickel is
toxic, and its release from nickel white gold is controlled by
legislation in Europe. Palladium-gold alloys are more expensive than
those using nickel. High-karat white gold alloys are more resistant to
corrosion than are either pure silver or sterling silver. The Japanese
craft of Mokume-gane exploits the color contrasts between laminated
colored gold alloys to produce decorative wood-grain effects.
By 2014, the gold jewelry industry was escalating despite a dip in
gold prices. Demand in the first quarter of 2014 pushed turnover to
$23.7 billion according to a World Gold Council report.
Gold solder is used for joining the components of gold jewelry by
high-temperature hard soldering or brazing. If the work is to be of
hallmarking quality, the gold solder alloy must match the fineness of
the work, and alloy formulas are manufactured to color-match yellow
and white gold. Gold solder is usually made in at least three
melting-point ranges referred to as Easy, Medium and Hard. By using
the hard, high-melting point solder first, followed by solders with
progressively lower melting points, goldsmiths can assemble complex
items with several separate soldered joints. Gold can also be made
into thread and used in embroidery.
Electronics
=============
Only 10% of the world consumption of new gold produced goes to
industry, but by far the most important industrial use for new gold is
in fabrication of corrosion-free electrical connectors in computers
and other electrical devices. For example, according to the World Gold
Council, a typical cell phone may contain 50 mg of gold, worth about
three dollars. But since nearly one billion cell phones are produced
each year, a gold value of US$2.82 in each phone adds to US$2.82
billion in gold from just this application. (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.
Besides sliding electrical contacts, gold is also used in electrical
contacts because of its resistance to corrosion, electrical
conductivity, ductility and lack of toxicity. 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.
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.
Medicine
==========
There are only two gold compounds currently employed as
pharmaceuticals in modern medicine (sodium aurothiomalate and
auranofin), used in the treatment of arthritis and other similar
conditions in the US due to their anti-inflammatory properties. These
drugs have been explored as a means to help to reduce the pain and
swelling of rheumatoid arthritis, and also (historically) against
tuberculosis and some parasites.
Some esotericists and forms of alternative medicine assign metallic
gold a healing power, against the scientific consensus.
Historically, metallic and gold compounds have long been used for
medicinal purposes. Gold, usually as the metal, is perhaps the most
anciently administered medicine (apparently by shamanic practitioners)
and known to Dioscorides. In medieval times, gold was often seen as
beneficial for the health, in the belief that something so rare and
beautiful could not be anything but healthy.
In the 19th century gold had a reputation as an anxiolytic, a therapy
for nervous disorders. Depression, epilepsy, migraine, and glandular
problems such as amenorrhea and impotence were treated, and most
notably alcoholism (Keeley, 1897).
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. 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).
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. In ultrathin sections of tissues viewed by electron
microscopy, the immunogold labels appear as extremely dense round
spots at the position of the antigen.
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.
The isotope gold-198 (half-life 2.7 days) is used in nuclear medicine,
in some cancer treatments and for treating other diseases.
Cuisine
=========
* Gold can be used in food and has the E number 175. 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.
* Gold leaf, flake or dust is used on and in some gourmet foods,
notably sweets and drinks as decorative ingredient. Gold flake was
used by the nobility in medieval Europe as a decoration in food and
drinks,
* Danziger Goldwasser (German: Gold water of Danzig) or Goldwasser ()
is a traditional German herbal liqueur 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.
* Vark is a foil composed of a pure metal that is sometimes gold, and
is used for garnishing sweets in South Asian cuisine.
Miscellanea
=============
* 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.
* 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.
* 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.
* 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.
* Gold, when dispersed in nanoparticles, can act as a heterogeneous
catalyst of chemical reactions.
* In recent years, gold has been used as a symbol of pride by the
autism rights movement, as its symbol Au could be seen as similar to
the word "autism".
Toxicity
======================================================================
Pure metallic (elemental) gold is non-toxic and non-irritating when
ingested and is sometimes used as a food decoration in the form of
gold leaf. 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. 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. Despite this, gold is a relatively non-potent contact allergen,
in comparison with metals like nickel.
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.
See also
======================================================================
* Bulk leach extractable gold, for sampling ores
* Chrysiasis (dermatological condition)
* Digital gold currency, form of electronic currency
* GFMS business consultancy
* Gold fingerprinting, use impurities to identify an alloy
* Gold standard in banking
* List of countries by gold production
* Tumbaga, alloy of gold and copper
* Iron pyrite, fool's gold
* Nordic gold, non-gold copper alloy
Further reading
======================================================================
* Bachmann, H. G. 'The lure of gold : an artistic and cultural
history' (2006) [
https://archive.org/details/lureofgold0000unse
online]
* Bernstein, Peter L. 'The Power of Gold: The History of an Obsession'
(2000) [
https://archive.org/details/powerofgoldhisto00bern online]
* Brands, H.W. 'The Age of Gold: The California Gold Rush and the New
American Dream' (2003)
[
https://www.amazon.com/Age-Gold-California-American-Recover/dp/0385720882/
excerpt]
* Buranelli, Vincent. 'Gold : an illustrated history' (1979)
[
https://archive.org/details/goldillustratedh00bura online]'
wide-ranging popular history
* Cassel, Gustav. "The restoration of the gold standard." 'Economica'
9 (1923): 171-185. [
https://www.jstor.org/stable/2548130 online]
* Eichengreen, Barry. 'Golden Fetters: The Gold Standard and the Great
Depression, 1919-1939' (Oxford UP, 1992).
* Ferguson, Niall. 'The Ascent of Money - Financial History of the
World' (2009) [
https://archive.org/details/ascentofmoneyf00ferg
online]
* Hart, Matthew, [
https://books.google.com/books?id=kSI5AAAAQBAJ Gold:
The Race for the World's Most Seductive Metal] 'Gold : the race for
the world's most seductive metal", New York: Simon & Schuster,
2013. '
*
* Kwarteng, Kwasi. 'War and Gold: A Five-Hundred-Year History of
Empires, Adventures, and Debt' (2014)
[
https://archive.org/details/wargoldfivehundr0000kwar online]
* Vilar, Pierre. 'A History of Gold and Money, 1450-1920' (1960).
[
https://archive.org/details/historyofgoldmon0000vila_c6t2 online]
* Vilches, Elvira. 'New World Gold: Cultural Anxiety and Monetary
Disorder in Early Modern Spain' (2010).
External links
======================================================================
*
*
[
https://web.archive.org/web/20080417110808/http://www.rsc.org/chemistryworld/podcast/element.asp
Chemistry in its element podcast] (MP3) from the Royal Society of
Chemistry's Chemistry World:
[
http://www.rsc.org/images/CIIE_Gold_48k_tcm18-118269.mp3 Gold]
www.rsc.org
* [
http://www.periodicvideos.com/videos/079.htm Gold] at 'The Periodic
Table of Videos' (University of Nottingham)
*
[
https://web.archive.org/web/20080307000911/http://www.epa.gov/epaoswer/other/mining/techdocs/gold.pdf
'Getting Gold' 1898 book], www.lateralscience.co.uk
* , www.epa.gov
* [
https://www.rsc.org/periodic-table/element/79/gold Gold element
information] - rsc.org
License
=========
All content on Gopherpedia comes from Wikipedia, and is licensed under CC-BY-SA
License URL:
http://creativecommons.org/licenses/by-sa/3.0/
Original Article:
http://en.wikipedia.org/wiki/Gold
