Gold

Gold

Overview
Gold is a chemical element
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...

 with the symbol Au (from "gold") and an atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...

 of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a transition metal
Transition metal
The term transition metal has two possible meanings:*The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Group 12 elements are not transition metals in this definition.*Some...

 and a group 11 element
Group 11 element
A Group 11 element is one in the series of elements in group 11 in the periodic table, consisting of transition metals which are the traditional coinage metals of copper , silver , and gold...

. It is one of the least reactive solid chemical elements. The metal therefore occurs often in free elemental (native) form, as nuggets
Gold nugget
A gold nugget is a naturally occurring piece of native gold. Watercourses often concentrate and grow the nuggets. Nuggets are recovered by placer mining, but they are also found in residual deposits where the gold-bearing veins or lodes are weathered...

 or grains in rocks, in veins
Vein (geology)
In geology, a vein is a distinct sheetlike body of crystallized minerals within a rock. Veins form when mineral constituents carried by an aqueous solution within the rock mass are deposited through precipitation...

 and in alluvial deposits.
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Timeline

631   Emperor Taizong of Tang, the Emperor of China, sends envoys to the Xueyantuo bearing gold and silk in order to seek the release of enslaved Chinese prisoners captured during the transition from Sui to Tang from the northern frontier; this embassy succeeded in freeing 80,000 Chinese men and women who were then returned to China.

1539   In Florida, Hernando de Soto lands at Tampa Bay with 600 soldiers with the goal of finding gold.

1848   California Gold Rush: James W. Marshall finds gold at Sutter's Mill near Sacramento.

1848   California Gold Rush: In a message before the U.S. Congress, US President James K. Polk confirms that large amounts of gold had been discovered in California.

1849   The U.S. Congress passes the Gold Coinage Act allowing the minting of gold coins.

1864   Helena, Montana is founded after four prospectors discover gold at "Last Chance Gulch".

1869   "Black Friday": Gold prices plummet after Ulysses S. Grant orders the Treasury to sell large quantities of gold after Jay Gould and James Fisk plot to control the market.

1926   Gold is discovered in Johannesburg, South Africa.

1933   The U.S. Congress abrogates the United States' use of the gold standard by enacting a joint resolution (48 Stat. 112) nullifying the right of creditors to demand payment in gold.

1938   Archaeologists discover engraved gold and silver plates from King Darius in Persepolis.

 
Encyclopedia
Gold is a chemical element
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...

 with the symbol Au (from "gold") and an atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...

 of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a transition metal
Transition metal
The term transition metal has two possible meanings:*The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Group 12 elements are not transition metals in this definition.*Some...

 and a group 11 element
Group 11 element
A Group 11 element is one in the series of elements in group 11 in the periodic table, consisting of transition metals which are the traditional coinage metals of copper , silver , and gold...

. It is one of the least reactive solid chemical elements. The metal therefore occurs often in free elemental (native) form, as nuggets
Gold nugget
A gold nugget is a naturally occurring piece of native gold. Watercourses often concentrate and grow the nuggets. Nuggets are recovered by placer mining, but they are also found in residual deposits where the gold-bearing veins or lodes are weathered...

 or grains in rocks, in veins
Vein (geology)
In geology, a vein is a distinct sheetlike body of crystallized minerals within a rock. Veins form when mineral constituents carried by an aqueous solution within the rock mass are deposited through precipitation...

 and in alluvial deposits. Less commonly, it occurs in minerals as gold compounds, usually with tellurium.

Gold resists attacks by individual acids, but it can be dissolved by the aqua regia
Aqua regia
Aqua regia or aqua regis is a highly corrosive mixture of acids, fuming yellow or red solution, also called nitro-hydrochloric acid. The mixture is formed by freshly mixing concentrated nitric acid and hydrochloric acid, usually in a volume ratio of 1:3, respectively...

 (nitro-hydrochloric acid), so named because it dissolves gold. Gold also dissolves in alkaline solutions of cyanide
Cyanide
A cyanide is a chemical compound that contains the cyano group, -C≡N, which consists of a carbon atom triple-bonded to a nitrogen atom. Cyanides most commonly refer to salts of the anion CN−. Most cyanides are highly toxic....

, which have been used in mining. Gold dissolves in mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

, forming amalgam
Amalgam (chemistry)
An amalgam is a substance formed by the reaction of mercury with another metal. Almost all metals can form amalgams with mercury, notable exceptions being iron and platinum. Silver-mercury amalgams are important in dentistry, and gold-mercury amalgam is used in the extraction of gold from ore.The...

 alloys. Gold is insoluble in nitric acid
Nitric acid
Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...

, which dissolves silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...

 and base metal
Base metal
In chemistry, the term base metal is used informally to refer to a metal that oxidizes or corrodes relatively easily, and reacts variably with diluted hydrochloric acid to form hydrogen. Examples include iron, nickel, lead and zinc...

s, a property that has long been used to confirm the presence of gold in items, giving rise to the term the acid test
Acid test (gold)
An acid test is any qualitative chemical or metallurgical assay which uses acid; most commonly, and historically, the use of a strong acid to distinguish gold from base metals. Figuratively, acid test is any definitive test for some attribute, e.g...

.


Gold has been a valuable and highly sought-after precious metal
Precious metal
A precious metal is a rare, naturally occurring metallic chemical element of high economic value.Chemically, the precious metals are less reactive than most elements, have high lustre, are softer or more ductile, and have higher melting points than other metals...

 for coin
Coin
A coin is a piece of hard material that is standardized in weight, is produced in large quantities in order to facilitate trade, and primarily can be used as a legal tender token for commerce in the designated country, region, or territory....

age, jewelry, and other arts since long before the beginning of recorded history
Recorded history
Recorded history is the period in history of the world after prehistory. It has been written down using language, or recorded using other means of communication. It starts around the 4th millennium BC, with the invention of writing.-Historical accounts:...

. Gold standard
Gold standard
The gold standard is a monetary system in which the standard economic unit of account is a fixed mass of gold. There are distinct kinds of gold standard...

s have been the most common basis for monetary policies
Monetary policy
Monetary policy is the process by which the monetary authority of a country controls the supply of money, often targeting a rate of interest for the purpose of promoting economic growth and stability. The official goals usually include relatively stable prices and low unemployment...

 throughout human history, being widely supplanted by fiat currency only in the late 20th century. Gold has also been frequently linked to a wide variety of symbolisms and ideologies. A total of 165,000 tonne
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...

s of gold have been mined in human history, as of 2009. This is roughly equivalent to 5.3 billion troy ounce
Troy ounce
The troy ounce is a unit of imperial measure. In the present day it is most commonly used to gauge the weight of precious metals. One troy ounce is nowadays defined as exactly 0.0311034768 kg = 31.1034768 g. There are approximately 32.1507466 troy oz in 1 kg...

s or, in terms of volume, about 8500 m3, or a cube
Cube
In geometry, a cube is a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex. The cube can also be called a regular hexahedron and is one of the five Platonic solids. It is a special kind of square prism, of rectangular parallelepiped and...

 20.4 m on a side. The world consumption of new gold produced is about 50% in jewelry, 40% in investments, and 10% in industry.

Besides its widespread monetary and symbolic functions, gold has many practical uses in dentistry
Dentistry
Dentistry is the branch of medicine that is involved in the study, diagnosis, prevention, and treatment of diseases, disorders and conditions of the oral cavity, maxillofacial area and the adjacent and associated structures and their impact on the human body. Dentistry is widely considered...

, electronics
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

, and other fields. Its high malleability, ductility
Ductility
In materials science, ductility is a solid material's ability to deform under tensile stress; this is often characterized by the material's ability to be stretched into a wire. Malleability, a similar property, is a material's ability to deform under compressive stress; this is often characterized...

, resistance to corrosion and most other chemical reactions, and conductivity of electricity led to many uses of gold, including electric wiring, colored-glass production and even gold leaf
Gold leaf
right|thumb|250px|[[Burnishing]] gold leaf with an [[agate]] stone tool, during the water gilding processGold leaf is gold that has been hammered into extremely thin sheets and is often used for gilding. Gold leaf is available in a wide variety of karats and shades...

 eating.

Characteristics


Gold is the most malleable and ductile
Ductility
In materials science, ductility is a solid material's ability to deform under tensile stress; this is often characterized by the material's ability to be stretched into a wire. Malleability, a similar property, is a material's ability to deform under compressive stress; this is often characterized...

 of all metals; a single gram can be beaten into a sheet of 1 square meter, or an ounce
Ounce
The ounce is a unit of mass with several definitions, the most commonly used of which are equal to approximately 28 grams. The ounce is used in a number of different systems, including various systems of mass that form part of the imperial and United States customary systems...

 into 300 square feet. Gold leaf can be beaten thin enough to become translucent. 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 visors of heat-resistant suits, and in sun-visors for spacesuits.

Gold readily creates alloys with many other metals. These alloys can be produced to modify the hardness and other metallurgical properties, to control melting point
Melting point
The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...

 or to create exotic colors (see below). Gold is a good conductor of heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

 and electricity
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...

 and reflects infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

 radiation strongly. Chemically, it is unaffected by air
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

, moisture
Moisture
Humidity is the amount of moisture the air can hold before it rains. Moisture refers to the presence of a liquid, especially water, often in trace amounts...

 and most corrosive
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...

 reagent
Reagent
A reagent is a "substance or compound that is added to a system in order to bring about a chemical reaction, or added to see if a reaction occurs." Although the terms reactant and reagent are often used interchangeably, a reactant is less specifically a "substance that is consumed in the course of...

s, and is therefore well suited for use in coin
Coin
A coin is a piece of hard material that is standardized in weight, is produced in large quantities in order to facilitate trade, and primarily can be used as a legal tender token for commerce in the designated country, region, or territory....

s and jewelry and as a protective coating on other, more reactive, metals. However, it is not chemically inert.

Common oxidation state
Oxidation state
In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...

s 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
Precipitation (chemistry)
Precipitation is the formation of a solid in a solution or inside anothersolid during a chemical reaction or by diffusion in a solid. When the reaction occurs in a liquid, the solid formed is called the precipitate, or when compacted by a centrifuge, a pellet. The liquid remaining above the solid...

 out as gold metal by adding any other metal as the reducing agent
Reducing agent
A reducing agent is the element or compound in a reduction-oxidation reaction that donates an electron to another species; however, since the reducer loses an electron we say it is "oxidized"...

. The added metal is oxidized and dissolves allowing the gold to be displaced from solution and be recovered as a solid precipitate.

High quality pure metallic gold is tasteless and scentless, in keeping with its resistance to corrosion (it is metal ions which confer taste to metals).

In addition, gold is very dense, a cubic meter weighing 19,300 kg. By comparison, the density of lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

 is 11,340 kg/m3, and that of the densest element, osmium
Osmium
Osmium is a chemical element with the symbol Os and atomic number 76. Osmium is a hard, brittle, blue-gray or blue-blacktransition metal in the platinum family, and is the densest natural element. Osmium is twice as dense as lead. The density of osmium is , slightly greater than that of iridium,...

, is 22,610 kg/m3.

Color



Whereas most other pure metals are gray or silvery white, gold is yellow. This color is determined by the density of loosely bound (valence) electrons; those electrons oscillate as a collective "plasma" medium described in terms of a quasiparticle
Quasiparticle
In physics, quasiparticles are emergent phenomena that occur when a microscopically complicated system such as a solid behaves as if it contained different weakly interacting particles in free space...

 called plasmon
Plasmon
In physics, a plasmon is a quantum of plasma oscillation. The plasmon is a quasiparticle resulting from the quantization of plasma oscillations just as photons and phonons are quantizations of light and mechanical vibrations, respectively...

. The frequency of these oscillations lies in the ultraviolet range for most metals, but it falls into the visible range for gold due to subtle relativistic effects
Relativistic quantum chemistry
Relativistic quantum chemistry invokes quantum chemical and relativistic mechanical arguments to explain elemental properties and structure, especially for heavy elements of the periodic table....

 that affect the orbitals
Atomic orbital
An atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus...

 around gold atoms. Similar effects impart a golden hue to metallic caesium
Caesium
Caesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C , which makes it one of only five elemental metals that are liquid at room temperature...

 (see relativistic quantum chemistry
Relativistic quantum chemistry
Relativistic quantum chemistry invokes quantum chemical and relativistic mechanical arguments to explain elemental properties and structure, especially for heavy elements of the periodic table....

).

Common colored gold
Colored gold
While pure gold is yellow in color, colored gold can be developed into various colors. These colors are generally obtained by alloying gold with other elements in various proportions....

 alloys such as rose gold can be created by the addition of various amounts of copper and silver, as indicated in the triangular diagram to the left. Alloys containing palladium or nickel are also important in commercial jewelry as these produce white gold alloys. Less commonly, addition of manganese
Manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...

, aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

, iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

, indium
Indium
Indium is a chemical element with the symbol In and atomic number 49. This rare, very soft, malleable and easily fusible post-transition metal is chemically similar to gallium and thallium, and shows the intermediate properties between these two...

 and other elements can produce more unusual colors of gold for various applications.

Isotopes



Gold has only one stable isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...

, 197Au, which is also its only naturally occurring isotope. Thirty-six radioisotopes have been synthesized ranging in atomic mass
Atomic mass
The atomic mass is the mass of a specific isotope, most often expressed in unified atomic mass units. The atomic mass is the total mass of protons, neutrons and electrons in a single atom....

 from 169 to 205. The most stable of these is 195Au with a half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...

 of 186.1 days. The least stable is 171Au, which decays by proton emission
Proton emission
Proton emission is a type of radioactive decay in which a proton is ejected from a nucleus. Proton emission can occur from high-lying excited states in a nucleus following a beta decay, in which case the process is known as beta-delayed proton emission, or can occur from the ground state of very...

 with a half-life of 30 µs. Most of gold's radioisotopes with atomic masses below 197 decay by some combination of proton emission
Proton emission
Proton emission is a type of radioactive decay in which a proton is ejected from a nucleus. Proton emission can occur from high-lying excited states in a nucleus following a beta decay, in which case the process is known as beta-delayed proton emission, or can occur from the ground state of very...

, α decay
Alpha decay
Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less...

, and β+ decay. The exceptions are 195Au, which decays by electron capture, and 196Au, 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 isomer
Nuclear isomer
A nuclear isomer is a metastable state of an atomic nucleus caused by the excitation of one or more of its nucleons . "Metastable" refers to the fact that these excited states have half-lives more than 100 to 1000 times the half-lives of the other possible excited nuclear states...

s have also been characterized, ranging in atomic mass from 170 to 200. Within that range, only 178Au, 180Au, 181Au, 182Au, and 188Au do not have isomers. Gold's most stable isomer is 198m2Au with a half-life of 2.27 days. Gold's least stable isomer is 177 m2Au with a half-life of only 7 ns. 184 m1Au has three decay paths: β+ decay, isomeric transition
Isomeric transition
An isomeric transition is a radioactive decay process that involves emission of a gamma ray from an atom where the nucleus is in an excited metastable state, referred to in its excited state, as a nuclear isomer....

, and alpha decay. No other isomer or isotope of gold has three decay paths.

Monetary exchange


Gold has been widely used throughout the world as a vehicle for monetary
Money
Money is any object or record that is generally accepted as payment for goods and services and repayment of debts in a given country or socio-economic context. The main functions of money are distinguished as: a medium of exchange; a unit of account; a store of value; and, occasionally in the past,...

 exchange, either by issuance and recognition of gold coin
Gold coin
A gold coin is a coin made mostly or entirely of gold. Gold has been used for coins practically since the invention of coinage, originally because of gold's intrinsic value...

s or other bare metal quantities, or through gold-convertible paper instruments by establishing gold standard
Gold standard
The gold standard is a monetary system in which the standard economic unit of account is a fixed mass of gold. There are distinct kinds of gold standard...

s in which the total value of issued money is represented in a store of gold reserves.

However, production has not grown in relation to the world's economies. Today, gold mining
Gold mining
Gold mining is the removal of gold from the ground. There are several techniques and processes by which gold may be extracted from the earth.-History:...

 output is declining. With the sharp growth of economies in the 20th century, and increasing foreign exchange, the world's gold reserve
Gold Reserve
Gold Reserve Inc. is a gold mining company with operations and mining property in Bolivar State, Venezuela.Founded in 1956, Gold Reserve Inc. is now headquartered in Spokane, Washington. The company has about ten employees at its Washington office and about 55 in Venezuela. Of these 55,...

s and their trading market have become a small fraction of all markets and fixed exchange rates of currencies to gold were no longer sustained. At the beginning of World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

 the warring nations moved to a fractional gold standard, inflating their currencies to finance the war effort. After World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

 gold was replaced by a system of convertible currency following the Bretton Woods system
Bretton Woods system
The Bretton Woods system of monetary management established the rules for commercial and financial relations among the world's major industrial states in the mid 20th century...

. Gold standards and the direct convertibility of currencies to gold have been abandoned by world governments, being replaced by fiat currency in their stead. Switzerland
Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....

 was the last country to tie its currency to gold; it backed 40% of its value until the Swiss joined the International Monetary Fund
International Monetary Fund
The International Monetary Fund is an organization of 187 countries, working to foster global monetary cooperation, secure financial stability, facilitate international trade, promote high employment and sustainable economic growth, and reduce poverty around the world...

 in 1999.

Pure gold is too soft for day-to-day monetary use and is typically hardened by alloying with copper, silver or other base metals. The gold content of alloys is measured in carats
Carat (purity)
The karat or carat is a unit of purity for gold alloys.- Measure :Karat purity is measured as 24 times the purity by mass:where...

 (k). Pure gold is designated as 24k. English gold coins intended for circulation from 1526 into the 1930s were typically a standard 22k alloy called crown gold
Crown gold
Crown gold is a 22 karat gold alloy, introduced in England for gold crown coin manufacture in 1526 . It is 22/24 = 0.91667 fine or 91.667% gold....

, for hardness (American gold coins for circulation after 1837 contained the slightly lower amount of 0.900 fine gold, or 21.6 kt).

Investment



Many holders of gold store it in form of bullion coins or bar
Gold bar
A gold bar is a quantity of refined metallic gold of any shape that is made by a bar producer meeting standard conditions of manufacture, labeling, and record keeping....

s as a hedge against inflation
Inflation
In economics, inflation is a rise in the general level of prices of goods and services in an economy over a period of time.When the general price level rises, each unit of currency buys fewer goods and services. Consequently, inflation also reflects an erosion in the purchasing power of money – a...

 or other economic disruptions. However, some economists do not believe gold serves as a hedge against inflation or currency depreciation.

The ISO 4217
ISO 4217
ISO 4217 is a standard published by the International Standards Organization, which delineates currency designators, country codes , and references to minor units in three tables:* Table A.1 – Current currency & funds code list...

 currency code of gold is XAU.

Modern bullion coin
Bullion coin
A bullion coin is a coin struck from precious metal and kept as a store of value or an investment, rather than used in day-to-day commerce. Investment coins are generally coins that have been minted after 1800, have a purity of not less than 900 thousandths and are or have been a legal tender in...

s for investment or collector purposes do not require good mechanical wear properties; they are typically fine gold at 24k, although the American Gold Eagle
American Gold Eagle
The American Gold Eagle is an official gold bullion coin of the United States. Authorized under the Gold Bullion Coin Act of 1985, it was first released by the United States Mint in 1986.- Details :...

, the British gold sovereign, and the South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...

n Krugerrand
Krugerrand
The Krugerrand is a South African gold coin, first minted in 1967 to help market South African gold. The coin, produced by the South African Mint, proved popular and by 1980 the Krugerrand accounted for 90% of the gold coin market. The name itself is a compound of Kruger and rand, the South...

 continue to be minted in 22k metal in historical tradition. The special issue Canadian Gold Maple Leaf
Canadian Gold Maple Leaf
The Canadian Gold Maple Leaf is the official bullion gold coin of Canada, and is produced by the Royal Canadian Mint. The brainchild of Walter Ott, it is one of the purest gold regular-issue coins in the world with a gold content of .9999 millesimal fineness , with some special issues .99999 fine...

 coin contains the highest purity gold of any bullion coin
Bullion coin
A bullion coin is a coin struck from precious metal and kept as a store of value or an investment, rather than used in day-to-day commerce. Investment coins are generally coins that have been minted after 1800, have a purity of not less than 900 thousandths and are or have been a legal tender in...

, at 99.999% or 0.99999, while the popular issue Canadian Gold Maple Leaf coin has a purity of 99.99%. Several other 99.99% pure gold coins are available. In 2006, the United States Mint
United States Mint
The United States Mint primarily produces circulating coinage for the United States to conduct its trade and commerce. The Mint was created by Congress with the Coinage Act of 1792, and placed within the Department of State...

 began production of the American Buffalo
American Buffalo (coin)
The American Buffalo, also known as a gold buffalo, is a 24-karat bullion coin first offered for sale by the United States Mint on June 22, 2006, and available for shipment beginning on July 13. The coin follows the greatly admired design of the Indian Head nickel and has gained its nickname from...

 gold bullion coin with a purity of 99.99%. The Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

n Gold Kangaroos were first coined in 1986 as the Australian Gold Nugget
Australian Gold Nugget
The Australian Gold Nugget is a gold bullion coin minted by the Perth Mint. The coins have been minted in denominations of 1/20 oz, 1/10 oz, 1/4 oz, 1/2 oz, 1 oz, 2 oz, 10 oz, and 1 kg of 24 carat gold...

 but changed the reverse design in 1989. Other popular modern coins include the Austria
Austria
Austria , officially the Republic of Austria , is a landlocked country of roughly 8.4 million people in Central Europe. It is bordered by the Czech Republic and Germany to the north, Slovakia and Hungary to the east, Slovenia and Italy to the south, and Switzerland and Liechtenstein to the...

n Vienna Philharmonic bullion coin and the Chinese Gold Panda
Chinese Gold Panda
The Chinese Gold Panda is a series of gold bullion coins issued by the People's Republic of China. The official mint of the People's Republic of China introduced the Panda gold bullion coins in 1982. The panda design changes every year and the gold Panda coins come in different sizes and...

.

Jewelry


Because of the softness of pure (24k) gold, it is usually alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...

ed with base metals for use in jewelry, altering its hardness and ductility, melting point, color and other properties. Alloys with lower caratage, typically 22k, 18k, 14k or 10k, contain higher percentages of copper, or other base metals or silver or palladium in the alloy. Copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

 is the most commonly used base metal, yielding a redder color. Eighteen-carat gold containing 25% copper is found in antique and Russian jewelry and has a distinct, though not dominant, copper cast, creating rose gold. Fourteen-carat gold-copper alloy is nearly identical in color to certain bronze
Bronze
Bronze is a metal alloy consisting primarily of copper, usually with tin as the main additive. It is hard and brittle, and it was particularly significant in antiquity, so much so that the Bronze Age was named after the metal...

 alloys, and both may be used to produce police and other badges. Blue gold can be made by alloying with iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 and purple gold can be made by alloying with aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

, although rarely done except in specialized jewelry. Blue gold is more brittle and therefore more difficult to work with when making jewelry. Fourteen and eighteen carat gold alloys with silver alone appear greenish-yellow and are referred to as green gold. White gold alloys can be made with palladium
Palladium
Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named after the epithet of the Greek goddess Athena, acquired...

 or nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...

. White 18-carat gold containing 17.3% nickel, 5.5% zinc and 2.2% copper is silvery in appearance. Nickel is toxic, however, and its release from nickel white gold is controlled by legislation in Europe. Alternative white gold alloys are available based on palladium, silver and other white metals, but the palladium alloys are more expensive than those using nickel. High-carat white gold alloys are far more resistant to corrosion than are either pure silver or sterling silver
Sterling silver
Sterling silver is an alloy of silver containing 92.5% by mass of silver and 7.5% by mass of other metals, usually copper. The sterling silver standard has a minimum millesimal fineness of 925....

. The Japanese craft of Mokume-gane
Mokume-gane
is a mixed-metal laminate with distinctive layered patterns. Translating as burl metal, the name was borrowed from one type of pattern created in the forging of swords and other edged weapons.- History :...

 exploits the color contrasts between laminated colored gold alloys to produce decorative wood-grain effects.

Medicine


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
Esotericism
Esotericism or Esoterism signifies the holding of esoteric opinions or beliefs, that is, ideas preserved or understood by a small group or those specially initiated, or of rare or unusual interest. The term derives from the Greek , a compound of : "within", thus "pertaining to the more inward",...

 and forms of alternative medicine
Alternative medicine
Alternative medicine is any healing practice, "that does not fall within the realm of conventional medicine." It is based on historical or cultural traditions, rather than on scientific evidence....

 assign metallic gold a healing power. Some gold salts do have anti-inflammatory
Anti-inflammatory
Anti-inflammatory refers to the property of a substance or treatment that reduces inflammation. Anti-inflammatory drugs make up about half of analgesics, remedying pain by reducing inflammation as opposed to opioids, which affect the central nervous system....

 properties and are used as pharmaceuticals in the treatment of arthritis and other similar conditions. However, only salts and radioisotopes of gold are of pharmacological value, as elemental (metallic) gold is inert to all chemicals it encounters inside the body. In modern times, injectable gold has been proven to help to reduce the pain and swelling of rheumatoid arthritis
Rheumatoid arthritis
Rheumatoid arthritis is a chronic, systemic inflammatory disorder that may affect many tissues and organs, but principally attacks synovial joints. The process produces an inflammatory response of the synovium secondary to hyperplasia of synovial cells, excess synovial fluid, and the development...

 and tuberculosis
Tuberculosis
Tuberculosis, MTB, or TB is a common, and in many cases lethal, infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis. Tuberculosis usually attacks the lungs but can also affect other parts of the body...

.

Gold alloys are used in restorative dentistry, especially in tooth restorations, such as crowns
Crown (dentistry)
A crown is a type of dental restoration which completely caps or encircles a tooth or dental implant. Crowns are often needed when a large cavity threatens the ongoing health of a tooth. They are typically bonded to the tooth using a dental cement. Crowns can be made from many materials, which...

 and permanent bridges
Bridge (dentistry)
A bridge, also known as a fixed partial denture, is a dental restoration used to replace a missing tooth by joining permanently to adjacent teeth or dental implants....

. 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
Colloidal gold
Colloidal gold is a suspension of sub-micrometre-sized particles of gold in a fluid — usually water. The liquid is usually either an intense red colour , or a dirty yellowish colour ....

 preparations (suspensions of gold nanoparticles) in water are intensely red-color
Color
Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors...

ed, and can be made with tightly controlled particle sizes up to a few tens of nanometers across by reduction of gold chloride with citrate
Citrate
A citrate can refer either to the conjugate base of citric acid, , or to the esters of citric acid. An example of the former, a salt is trisodium citrate; an ester is triethyl citrate.-Other citric acid ions:...

 or ascorbate ions. Colloidal gold is used in research applications in medicine, biology and materials science
Materials science
Materials science is an interdisciplinary field applying the properties of matter to various areas of science and engineering. This scientific field investigates the relationship between the structure of materials at atomic or molecular scales and their macroscopic properties. It incorporates...

. 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
Electron microscope
An electron microscope is a type of microscope that uses a beam of electrons to illuminate the specimen and produce a magnified image. Electron microscopes have a greater resolving power than a light-powered optical microscope, because electrons have wavelengths about 100,000 times shorter than...

, the immunogold labels appear as extremely dense round spots at the position of the antigen
Antigen
An antigen is a foreign molecule that, when introduced into the body, triggers the production of an antibody by the immune system. The immune system will then kill or neutralize the antigen that is recognized as a foreign and potentially harmful invader. These invaders can be molecules such as...

. Colloidal gold is also the form of gold used as gold paint on ceramic
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...

s prior to firing.

Gold, or alloys of gold and palladium
Palladium
Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named after the epithet of the Greek goddess Athena, acquired...

, 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
Scanning electron microscope
A scanning electron microscope is a type of electron microscope that images a sample by scanning it with a high-energy beam of electrons in a raster scan pattern...

. The coating, which is usually applied by sputtering
Sputtering
Sputtering is a process whereby atoms are ejected from a solid target material due to bombardment of the target by energetic particles. It is commonly used for thin-film deposition, etching and analytical techniques .-Physics of sputtering:...

 with an argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...

 plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...

, has a triple role in this application. Gold's very high electrical conductivity drains electrical charge
Electric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...

 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
Angular resolution
Angular resolution, or spatial resolution, describes the ability of any image-forming device such as an optical or radio telescope, a microscope, a camera, or an eye, to distinguish small details of an object...

 of the image. Gold also produces a high output of secondary electrons
Secondary emission
Secondary emission in physics is a phenomenon where primary incident particles of sufficient energy, when hitting a surface or passing through some material, induce the emission of secondary particles. The primary particles are often charged particles like electrons or ions. If the secondary...

 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
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...

 2.7 days) is used in some cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...

 treatments and for treating other diseases.

Food and drink

  • Gold can be used in food and has the E number
    E number
    E numbers are number codes for food additives that have been assessed for use within the European Union . They are commonly found on food labels throughout the European Union. Safety assessment and approval are the responsibility of the European Food Safety Authority...

     175.
  • Gold leaf
    Gold leaf
    right|thumb|250px|[[Burnishing]] gold leaf with an [[agate]] stone tool, during the water gilding processGold leaf is gold that has been hammered into extremely thin sheets and is often used for gilding. Gold leaf is available in a wide variety of karats and shades...

    , 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, 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.
  • Danziger Goldwasser (German: Gold water of Danzig) or Goldwasser
    Goldwasser
    Danziger Goldwasser ), with Goldwasser as the registered tradename, is a strong root and herbal liqueur which has been produced since at least 1598 in Danzig ....

     (Goldwater) is a traditional German herbal liqueur
    Liqueur
    A liqueur is an alcoholic beverage that has been flavored with fruit, herbs, nuts, spices, flowers, or cream and bottled with added sugar. Liqueurs are typically quite sweet; they are usually not aged for long but may have resting periods during their production to allow flavors to marry.The...

     produced in what is today Gdańsk
    Gdansk
    Gdańsk is a Polish city on the Baltic coast, at the centre of the country's fourth-largest metropolitan area.The city lies on the southern edge of Gdańsk Bay , in a conurbation with the city of Gdynia, spa town of Sopot, and suburban communities, which together form a metropolitan area called the...

    , Poland
    Poland
    Poland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...

    , and Schwabach
    Schwabach
    Schwabach is a German town of about 40,000 inhabitants near Nuremberg, in the center of the region of Franconia in the North of Bavaria. The city is an autonomous administrative district . Schwabach is also the name of a river which runs through the city prior joining the Rednitz.Schwabach is...

    , Germany, and contains flakes of gold leaf. There are also some expensive (~$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.

Industry


  • Gold solder
    Solder
    Solder is a fusible metal alloy used to join together metal workpieces and having a melting point below that of the workpiece.Soft solder is what is most often thought of when solder or soldering are mentioned and it typically has a melting range of . It is commonly used in electronics and...

     is used for joining the components of gold jewelry by high-temperature hard soldering or brazing
    Brazing
    Brazing is a metal-joining process whereby a filler metal is heated above and distributed between two or more close-fitting parts by capillary action. The filler metal is brought slightly above its melting temperature while protected by a suitable atmosphere, usually a flux...

    . If the work is to be of hallmark
    Hallmark
    A hallmark is an official mark or series of marks struck on items made of precious metals — platinum, gold, silver and in some nations, palladium...

    ing quality, gold solder must match the carat weight of the work, and alloy formulas are manufactured in most industry-standard carat weights 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 be made into thread and used in embroidery
    Embroidery
    Embroidery is the art or handicraft of decorating fabric or other materials with needle and thread or yarn. Embroidery may also incorporate other materials such as metal strips, pearls, beads, quills, and sequins....

    .
  • Gold produces a deep, intense red color when used as a coloring agent in cranberry glass
    Cranberry glass
    Cranberry glass is a red glass made by adding gold chloride to molten glass. Tin, in the form of stannous chloride, is sometimes added in tiny amounts as a reducing agent...

    .
  • In photography, gold toners are used to shift the color of silver bromide
    Silver bromide
    Silver bromide , a soft, pale-yellow, water insoluble salt well known for its unusual sensitivity to light. This property has allowed silver halides to become the basis of modern photographic materials. AgBr is widely used in photographic films and is believed by some to have been used for making...

     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.
  • As gold is a good reflector of electromagnetic radiation
    Electromagnetic radiation
    Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...

     such as infrared and visible light
    Visible spectrum
    The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 390 to 750 nm. In terms of...

     as well as radio waves
    Radio frequency
    Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...

    , it is used for the protective coatings on many artificial satellite
    Satellite
    In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....

    s, in infrared protective faceplates in thermal protection suits and astronauts' helmets and in electronic warfare
    Electronic warfare
    Electronic warfare refers to any action involving the use of the electromagnetic spectrum or directed energy to control the spectrum, attack an enemy, or impede enemy assaults via the spectrum. The purpose of electronic warfare is to deny the opponent the advantage of, and ensure friendly...

     planes like the EA-6B Prowler.
  • Gold is used as the reflective layer on some high-end CDs
    Gold CD
    A gold CD is one in which gold is used in place of the super purity aluminiumcommonly used as the reflective coating on ordinary CDs or silver on ordinary CD-RsThe gold coats more evenly and reacts with oxygen more slowly, thus...

    .
  • Automobiles may use gold for heat dissipation. McLaren
    McLaren
    McLaren Racing Limited, trading as Vodafone McLaren Mercedes, is a British Formula One team based in Woking, Surrey, United Kingdom. McLaren is best known as a Formula One constructor but has also competed and won in the Indianapolis 500 and Canadian-American Challenge Cup...

     uses gold foil in the engine compartment of its F1
    McLaren F1
    The McLaren F1 is a supercar designed and manufactured by McLaren Automotive. Originally a concept conceived by Gordon Murray, he convinced Ron Dennis to back the project and engaged Peter Stevens to design the exterior of the car...

     model.
  • Gold can be manufactured so thin that it appears transparent. It is used in some aircraft cockpit windows for de-icing
    Deicing
    For snow and ice control on roadways and similar facilities, see Snow removalDe-icing is defined as removal of snow, ice or frost from a surface...

     or anti-icing by passing electricity through it. The heat produced by the resistance of the gold is enough to deter ice from forming.

Electronics


The concentration of free electrons in gold metal is 5.90×1022 cm−3. Gold is highly conductive to electricity, and has been used for electrical wiring
Electrical wiring
Electrical wiring in general refers to insulated conductors used to carry electricity, and associated devices. This article describes general aspects of electrical wiring as used to provide power in buildings and structures, commonly referred to as building wiring. This article is intended to...

 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
Manhattan Project
The Manhattan Project was a research and development program, led by the United States with participation from the United Kingdom and Canada, that produced the first atomic bomb during World War II. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the US Army...

's atomic experiments, but large high current silver wires were used in the calutron
Calutron
A calutron is a mass spectrometer used for separating the isotopes of uranium. It was developed by Ernest O. Lawrence during the Manhattan Project and was similar to the cyclotron invented by Lawrence. Its name is a concatenation of Cal. U.-tron, in tribute to the University of California,...

 isotope separator magnets in the project.

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 electrical connector
Electrical connector
An electrical connector is an electro-mechanical device for joining electrical circuits as an interface using a mechanical assembly. The connection may be temporary, as for portable equipment, require a tool for assembly and removal, or serve as a permanent electrical joint between two wires or...

s of all kinds, 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
Tin
Tin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead and has two possible oxidation states, +2 and the slightly more stable +4...

 in these applications is highly 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 computer
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...

s, communications equipment, spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....

, jet aircraft
Jet aircraft
A jet aircraft is an aircraft propelled by jet engines. Jet aircraft generally fly much faster than propeller-powered aircraft and at higher altitudes – as high as . At these altitudes, jet engines achieve maximum efficiency over long distances. The engines in propeller-powered aircraft...

 engines) remains very common.

Besides sliding electrical contacts, gold is also used in electrical contacts because of its resistance to corrosion
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...

, electrical conductivity, ductility and lack of toxicity
Toxicity
Toxicity is the degree to which a substance can damage a living or non-living organisms. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a substructure of the organism, such as a cell or an organ , such as the liver...

. Switch contacts are generally subjected to more intense corrosion stress than are sliding contacts. Fine gold wires are used to connect semiconductor device
Semiconductor device
Semiconductor devices are electronic components that exploit the electronic properties of semiconductor materials, principally silicon, germanium, and gallium arsenide, as well as organic semiconductors. Semiconductor devices have replaced thermionic devices in most applications...

s to their packages through a process known as wire bonding
Wire bonding
Wire bonding is the primary method of making interconnections between an integrated circuit and a printed circuit board during semiconductor device fabrication. Although less common, wire bonding can be used to connect an IC to other electronics or to connect from one PCB to another...

.

Commercial chemistry


Gold is attacked by and dissolves in alkaline solutions of potassium or sodium cyanide
Cyanide
A cyanide is a chemical compound that contains the cyano group, -C≡N, which consists of a carbon atom triple-bonded to a nitrogen atom. Cyanides most commonly refer to salts of the anion CN−. Most cyanides are highly toxic....

, 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
Electrolyte
In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....

 used in commercial electroplating
Electroplating
Electroplating is a plating process in which metal ions in a solution are moved by an electric field to coat an electrode. The process uses electrical current to reduce cations of a desired material from a solution and coat a conductive object with a thin layer of the material, such as a metal...

 of gold onto base metals and electroforming
Electroforming
Electroforming is a metal forming process that forms thin parts through the electroplating process. The part is produced by plating a metal skin onto a base form, known as a mandrel, which is removed after plating...

.

Gold chloride (chloroauric acid
Chloroauric acid
Chloroauric acid is a inorganic compound with the formula HAuCl4. This pale yellow compound is a common precursor to gold in a variety of purposes. The term chloroauric acid is also sometimes used to describe other gold chlorides....

) solutions are used to make colloidal gold by reduction with citrate
Citrate
A citrate can refer either to the conjugate base of citric acid, , or to the esters of citric acid. An example of the former, a salt is trisodium citrate; an ester is triethyl citrate.-Other citric acid ions:...

 or ascorbate ions. Gold chloride and gold oxide are used to make highly valued cranberry or red-colored glass, which, like colloid
Colloid
A colloid is a substance microscopically dispersed evenly throughout another substance.A colloidal system consists of two separate phases: a dispersed phase and a continuous phase . A colloidal system may be solid, liquid, or gaseous.Many familiar substances are colloids, as shown in the chart below...

al gold suspensions, contains evenly sized spherical gold nanoparticle
Nanoparticle
In nanotechnology, a particle is defined as a small object that behaves as a whole unit in terms of its transport and properties. Particles are further classified according to size : in terms of diameter, coarse particles cover a range between 10,000 and 2,500 nanometers. Fine particles are sized...

s.

History


Gold has been known and used by artisans since the Chalcolithic. Gold artifacts in the Balkans
Balkans
The Balkans is a geopolitical and cultural region of southeastern Europe...

 appear from the 4th millennium BC, such as those found in the Varna Necropolis
Varna Necropolis
The Varna Necropolis is a burial site in the western industrial zone of Varna , Bulgaria, internationally considered one of the key archaeological sites in world prehistory...

, Bulgaria
Bulgaria
Bulgaria , officially the Republic of Bulgaria , is a parliamentary democracy within a unitary constitutional republic in Southeast Europe. The country borders Romania to the north, Serbia and Macedonia to the west, Greece and Turkey to the south, as well as the Black Sea to the east...

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

Egyptian hieroglyphs from as early as 2600 BC describe gold, which king Tushratta
Tushratta
Tushratta was a king of Mitanni at the end of the reign of Amenhotep III and throughout the reign of Akhenaten -- approximately the late 14th century BC. He was the son of Shuttarna II...

 of the Mitanni
Mitanni
Mitanni or Hanigalbat was a loosely organized Hurrian-speaking state in northern Syria and south-east Anatolia from ca. 1500 BC–1300 BC...

 claimed was "more plentiful than dirt" in Egypt. Egypt and especially Nubia
Nubia
Nubia is a region along the Nile river, which is located in northern Sudan and southern Egypt.There were a number of small Nubian kingdoms throughout the Middle Ages, the last of which collapsed in 1504, when Nubia became divided between Egypt and the Sennar sultanate resulting in the Arabization...

 had the resources to make them major gold-producing areas for much of history. The earliest known map is known as the Turin Papyrus Map
Turin Papyrus Map
The Turin Papyrus Map is an ancient Egyptian map, generally considered the oldest surviving map of topographical interest from the ancient world. It is drawn on a papyrus reportedly discovered at Deir el-Medina in Thebes, collected by Bernardino Drovetti in Egypt sometime before 1824 AD and now...

 and shows the plan of a gold mine in Nubia together with indications of the local geology
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...

. The primitive working methods are described by both Strabo
Strabo
Strabo, also written Strabon was a Greek historian, geographer and philosopher.-Life:Strabo was born to an affluent family from Amaseia in Pontus , a city which he said was situated the approximate equivalent of 75 km from the Black Sea...

 and Diodorus Siculus
Diodorus Siculus
Diodorus Siculus was a Greek historian who flourished between 60 and 30 BC. According to Diodorus' own work, he was born at Agyrium in Sicily . With one exception, antiquity affords no further information about Diodorus' life and doings beyond what is to be found in his own work, Bibliotheca...

, and included fire-setting
Fire-setting
Fire-setting is a method of mining used since prehistoric times up to the Middle Ages. Fires were set against a rock face to heat the stone, which was then doused with water...

. Large mines were also present across the Red Sea
Red Sea
The Red Sea is a seawater inlet of the Indian Ocean, lying between Africa and Asia. The connection to the ocean is in the south through the Bab el Mandeb strait and the Gulf of Aden. In the north, there is the Sinai Peninsula, the Gulf of Aqaba, and the Gulf of Suez...

 in what is now Saudi Arabia
Saudi Arabia
The Kingdom of Saudi Arabia , commonly known in British English as Saudi Arabia and in Arabic as as-Sa‘ūdiyyah , is the largest state in Western Asia by land area, constituting the bulk of the Arabian Peninsula, and the second-largest in the Arab World...

.

The legend of the golden fleece
Golden Fleece
In Greek mythology, the Golden Fleece is the fleece of the gold-haired winged ram, which can be procured in Colchis. It figures in the tale of Jason and his band of Argonauts, who set out on a quest by order of King Pelias for the fleece in order to place Jason rightfully on the throne of Iolcus...

 may refer to the use of fleeces to trap gold dust from placer deposit
Placer deposit
In geology, a placer deposit or placer is an accumulation of valuable minerals formed by gravity separation during sedimentary processes. The name is from the Spanish word placer, meaning "alluvial sand". Placer mining is an important source of gold, and was the main technique used in the early...

s in the ancient world. Gold is mentioned frequently in the Old Testament
Old Testament
The Old Testament, of which Christians hold different views, is a Christian term for the religious writings of ancient Israel held sacred and inspired by Christians which overlaps with the 24-book canon of the Masoretic Text of Judaism...

, starting with Genesis 2:11 (at Havilah
Havilah
Havilah is in several books of the Bible referring to both land and people.The story of the Garden of Eden in Genesis 2:11: "And a river went out of Eden to water the garden; and from thence it was parted, and became into four heads...

) and is included with the gifts of the magi
Magi
Magi is a term, used since at least the 4th century BC, to denote a follower of Zoroaster, or rather, a follower of what the Hellenistic world associated Zoroaster with, which...

 in the first chapters of Matthew New Testament
New Testament
The New Testament is the second major division of the Christian biblical canon, the first such division being the much longer Old Testament....

. The Book of Revelation
Book of Revelation
The Book of Revelation is the final book of the New Testament. The title came into usage from the first word of the book in Koine Greek: apokalupsis, meaning "unveiling" or "revelation"...

 21:21 describes the city of New Jerusalem
New Jerusalem
In the book of Ezekiel, the Prophecy of New Jerusalem is Ezekiel's prophetic vision of a city to be established to the south of the Temple Mount that will be inhabited by the twelve tribes of Israel in the...

 as having streets "made of pure gold, clear as crystal". The south-east corner of the Black Sea
Black Sea
The Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean...

 was famed for its gold. Exploitation is said to date from the time of Midas
Midas
For the legend of Gordias, a person who was taken by the people and made King, in obedience to the command of the oracle, see Gordias.Midas or King Midas is popularly remembered in Greek mythology for his ability to turn everything he touched into gold. This was called the Golden touch, or the...

, and this gold was important in the establishment of what is probably the world's earliest coinage in Lydia
Lydia
Lydia was an Iron Age kingdom of western Asia Minor located generally east of ancient Ionia in the modern Turkish provinces of Manisa and inland İzmir. Its population spoke an Anatolian language known as Lydian....

 around 610 BC. From the 6th or 5th century BC, the Chu (state)
Chu (state)
The State of Chu was a Zhou Dynasty vassal state in present-day central and southern China during the Spring and Autumn period and Warring States Period . Its ruling house had the surname Nai , and clan name Yan , later evolved to surname Mi , and clan name Xiong...

 circulated the Ying Yuan
Ying Yuan
Ying Yuan is one kind of gold coin issued by the mint of the Chinese state of Chu. The oldest ones presently known are from about the 5th or 6th century BCE.-External links:*...

, one kind of square gold coin.

In Roman metallurgy
Roman metallurgy
Metals and metal working had been known to the people of modern Italy since the Bronze Age. By 86 BC, Rome had already expanded to control an immense expanse of the Mediterranean...

, new methods for extracting gold on a large scale were developed by introducing hydraulic mining
Hydraulic mining
Hydraulic mining, or hydraulicking, is a form of mining that uses high-pressure jets of water to dislodge rock material or move sediment. In the placer mining of gold or tin, the resulting water-sediment slurry is directed through sluice boxes to remove the gold.-Precursor - ground...

 methods, especially in Hispania
Hispania
Another theory holds that the name derives from Ezpanna, the Basque word for "border" or "edge", thus meaning the farthest area or place. Isidore of Sevilla considered Hispania derived from Hispalis....

 from 25 BC onwards and in Dacia
Dacia
In ancient geography, especially in Roman sources, Dacia was the land inhabited by the Dacians or Getae as they were known by the Greeks—the branch of the Thracians north of the Haemus range...

 from 106 AD onwards. One of their largest mines was at Las Medulas
Las Médulas
Las Médulas is a historical site near the town of Ponferrada in the region of El Bierzo , which used to be the most important gold mine in the Roman Empire...

 in León (Spain)
León (province)
León is a province of northwestern Spain, in the northwestern part of the autonomous community of Castile and León.About one quarter of its population of 500,200 lives in the capital, León. The weather is cold and dry during the winter....

, where seven long aqueduct
Aqueduct
An aqueduct is a water supply or navigable channel constructed to convey water. In modern engineering, the term is used for any system of pipes, ditches, canals, tunnels, and other structures used for this purpose....

s enabled them to sluice most of a large alluvial deposit. The mines at Roşia Montană
Rosia Montana
Roșia Montană is a commune of Alba County in the Apuseni Mountains of western Transylvania, Romania. It is located in the Valea Roșiei, through which the Roșia River flows...

 in Transylvania
Transylvania
Transylvania is a historical region in the central part of Romania. Bounded on the east and south by the Carpathian mountain range, historical Transylvania extended in the west to the Apuseni Mountains; however, the term sometimes encompasses not only Transylvania proper, but also the historical...

 were also very large, and until very recently, still mined by opencast methods. They also exploited smaller deposits in Britain
Roman Britain
Roman Britain was the part of the island of Great Britain controlled by the Roman Empire from AD 43 until ca. AD 410.The Romans referred to the imperial province as Britannia, which eventually comprised all of the island of Great Britain south of the fluid frontier with Caledonia...

, such as placer and hard-rock deposits at Dolaucothi. The various methods they used are well described by Pliny the Elder
Pliny the Elder
Gaius Plinius Secundus , better known as Pliny the Elder, was a Roman author, naturalist, and natural philosopher, as well as naval and army commander of the early Roman Empire, and personal friend of the emperor Vespasian...

 in his encyclopedia
Encyclopedia
An encyclopedia is a type of reference work, a compendium holding a summary of information from either all branches of knowledge or a particular branch of knowledge....

 Naturalis Historia
Naturalis Historia
The Natural History is an encyclopedia published circa AD 77–79 by Pliny the Elder. It is one of the largest single works to have survived from the Roman Empire to the modern day and purports to cover the entire field of ancient knowledge, based on the best authorities available to Pliny...

 written towards the end of the first century AD.

The Mali Empire
Mali Empire
The Mali Empire or Mandingo Empire or Manden Kurufa was a West African empire of the Mandinka from c. 1230 to c. 1600. The empire was founded by Sundiata Keita and became renowned for the wealth of its rulers, especially Mansa Musa I...

 in Africa was famed throughout the old world
Old World
The Old World consists of those parts of the world known to classical antiquity and the European Middle Ages. It is used in the context of, and contrast with, the "New World" ....

 for its large amounts of gold. Mansa Musa
Mansa Musa
Musa I , commonly referred to as Mansa Musa, was the tenth mansa, which translates as "king of kings" or "emperor", of the Malian Empire...

, ruler of the empire (1312–1337) became famous throughout the old world for his great hajj
Hajj
The Hajj is the pilgrimage to Mecca, Saudi Arabia. It is one of the largest pilgrimages in the world, and is the fifth pillar of Islam, a religious duty that must be carried out at least once in their lifetime by every able-bodied Muslim who can afford to do so...

 to Mecca
Mecca
Mecca is a city in the Hijaz and the capital of Makkah province in Saudi Arabia. The city is located inland from Jeddah in a narrow valley at a height of above sea level...

 in 1324. When he passed through Cairo
Cairo
Cairo , is the capital of Egypt and the largest city in the Arab world and Africa, and the 16th largest metropolitan area in the world. Nicknamed "The City of a Thousand Minarets" for its preponderance of Islamic architecture, Cairo has long been a centre of the region's political and cultural life...

 in July 1324, he was reportedly accompanied by a camel train
Camel train
A camel train is a series of camels carrying goods or passengers in a group as part of a regular or semi-regular service between two points. Although they rarely travelled faster than the walking speed of a man, camels' ability to handle harsh conditions made camel trains a vital part of...

 that included thousands of people and nearly a hundred camels. He gave away so much gold that it depressed the price in Egypt for over a decade. 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
Indigenous peoples of the Americas
The indigenous peoples of the Americas are the pre-Columbian inhabitants of North and South America, their descendants and other ethnic groups who are identified with those peoples. Indigenous peoples are known in Canada as Aboriginal peoples, and in the United States as Native Americans...

 peoples, especially in Central America
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...

, Peru
Peru
Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....

, Ecuador
Ecuador
Ecuador , officially the Republic of Ecuador is a representative democratic republic in South America, bordered by Colombia on the north, Peru on the east and south, and by the Pacific Ocean to the west. It is one of only two countries in South America, along with Chile, that do not have a border...

 and Colombia
Colombia
Colombia, officially the Republic of Colombia , is a unitary constitutional republic comprising thirty-two departments. The country is located in northwestern South America, bordered to the east by Venezuela and Brazil; to the south by Ecuador and Peru; to the north by the Caribbean Sea; to the...

. The Aztec
Aztec
The Aztec people were certain ethnic groups of central Mexico, particularly those groups who spoke the Nahuatl language and who dominated large parts of Mesoamerica in the 14th, 15th and 16th centuries, a period referred to as the late post-classic period in Mesoamerican chronology.Aztec is the...

s regarded gold as literally the product of the gods, calling it "god excrement" (teocuitlatl in Nahuatl
Nahuatl
Nahuatl is thought to mean "a good, clear sound" This language name has several spellings, among them náhuatl , Naoatl, Nauatl, Nahuatl, Nawatl. In a back formation from the name of the language, the ethnic group of Nahuatl speakers are called Nahua...

). However, for the indigenous peoples
Indigenous peoples
Indigenous peoples are ethnic groups that are defined as indigenous according to one of the various definitions of the term, there is no universally accepted definition but most of which carry connotations of being the "original inhabitants" of a territory....

 of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

, gold was considered useless, and they saw much greater value in other minerals, which were directly related to their utility, such as obsidian
Obsidian
Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock.It is produced when felsic lava extruded from a volcano cools rapidly with minimum crystal growth...

, flint
Flint
Flint is a hard, sedimentary cryptocrystalline form of the mineral quartz, categorized as a variety of chert. It occurs chiefly as nodules and masses in sedimentary rocks, such as chalks and limestones. Inside the nodule, flint is usually dark grey, black, green, white, or brown in colour, and...

, and slate
Slate
Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. The result is a foliated rock in which the foliation may not correspond to the original sedimentary layering...

.

Although the price of some platinum
Platinum
Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...

 group metals can be much higher, gold has long been considered the most desirable of precious metal
Precious metal
A precious metal is a rare, naturally occurring metallic chemical element of high economic value.Chemically, the precious metals are less reactive than most elements, have high lustre, are softer or more ductile, and have higher melting points than other metals...

s, and its value has been used as the standard for many currencies
Currency
In economics, currency refers to a generally accepted medium of exchange. These are usually the coins and banknotes of a particular government, which comprise the physical aspects of a nation's money supply...

 (known as the gold standard
Gold standard
The gold standard is a monetary system in which the standard economic unit of account is a fixed mass of gold. There are distinct kinds of gold standard...

) in history. 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
Thomas More
Sir Thomas More , also known by Catholics as Saint Thomas More, was an English lawyer, social philosopher, author, statesman and noted Renaissance humanist. He was an important councillor to Henry VIII of England and, for three years toward the end of his life, Lord Chancellor...

 in his treatise Utopia
Utopia (book)
Utopia is a work of fiction by Thomas More published in 1516...

. 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.

There is an age-old tradition of biting gold to test its authenticity. Although this is certainly not a professional way of examining gold, the bite test should score the gold because gold is a soft metal, as indicated by its score on the Mohs' scale of mineral hardness. The purer the gold the easier it should be to mark it. Painted lead can cheat this test because lead is softer than gold (and may invite a small risk of lead poisoning
Lead poisoning
Lead poisoning is a medical condition caused by increased levels of the heavy metal lead in the body. Lead interferes with a variety of body processes and is toxic to many organs and tissues including the heart, bones, intestines, kidneys, and reproductive and nervous systems...

 if sufficient lead is absorbed by the biting).

Gold in antiquity was relatively easy to obtain geologically
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...

; however, 75% of all gold ever produced has been extracted since 1910. It has been estimated that all gold ever refined would form a single cube 20 m (66 ft) on a side (equivalent to 8,000 m3).

One main goal of the alchemists
Alchemy
Alchemy is an influential philosophical tradition whose early practitioners’ claims to profound powers were known from antiquity. The defining objectives of alchemy are varied; these include the creation of the fabled philosopher's stone possessing powers including the capability of turning base...

 was to produce gold from other substances, such as lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

 — presumably by the interaction with a mythical substance called the philosopher's stone
Philosopher's stone
The philosopher's stone is a legendary alchemical substance said to be capable of turning base metals into gold or silver. It was also sometimes believed to be an elixir of life, useful for rejuvenation and possibly for achieving immortality. For many centuries, it was the most sought-after goal...

. Although they never succeeded in this attempt, the alchemists promoted an interest in what can be done with substances, and this laid a foundation for today's chemistry
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....

. Their symbol for gold was the circle with a point at its center (☉), which was also the astrological
Astrology
Astrology consists of a number of belief systems which hold that there is a relationship between astronomical phenomena and events in the human world...

 symbol and the ancient Chinese character
Chinese character
Chinese characters are logograms used in the writing of Chinese and Japanese , less frequently Korean , formerly Vietnamese , or other languages...

 for the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

. For modern creation of artificial gold by neutron capture
Neutron capture
Neutron capture is a kind of nuclear reaction in which an atomic nucleus collides with one or more neutrons and they merge to form a heavier nucleus. Since neutrons have no electric charge they can enter a nucleus more easily than positively charged protons, which are repelled...

, see gold synthesis.

During the 19th century, gold rush
Gold rush
A gold rush is a period of feverish migration of workers to an area that has had a dramatic discovery of gold. Major gold rushes took place in the 19th century in Australia, Brazil, Canada, South Africa, and the United States, while smaller gold rushes took place elsewhere.In the 19th and early...

es occurred whenever large gold deposits were discovered. The first documented discovery of gold in the United States was at the Reed Gold Mine
Reed Gold Mine
The Reed Gold Mine is located in Midland, Cabarrus County, North Carolina, and is the site of the first documented commercial gold find in the United States...

 near Georgeville, North Carolina in 1803. The first major gold strike in the United States occurred in a small north Georgia town called Dahlonega
Dahlonega, Georgia
Dahlonega is a city in Lumpkin County, Georgia, United States, and is its county seat. As of the 2010 census, the city had a population of 5,242....

. Further gold rushes occurred in California
California Gold Rush
The California Gold Rush began on January 24, 1848, when gold was found by James W. Marshall at Sutter's Mill in Coloma, California. The first to hear confirmed information of the gold rush were the people in Oregon, the Sandwich Islands , and Latin America, who were the first to start flocking to...

, Colorado, the Black Hills
Black Hills Gold Rush
The Black Hills Gold Rush took place in Dakota Territory in the United States. It began in 1874 following the Custer Expedition and reached a peak in 1876-77.Rumors and poorly documented reports of gold in the Black Hills go back to the early 19th century...

, Otago
Central Otago Gold Rush
The Central Otago Gold Rush was a gold rush that occurred during the 1860s in Central Otago, New Zealand...

 in New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

, Australia
Australian gold rushes
The Australian gold rush started in 1851 when prospector Edward Hammond Hargraves claimed the discovery of payable gold near Bathurst, New South Wales, at a site Edward Hargraves called Ophir.Eight months later, gold was found in Victoria...

, Witwatersrand
Witwatersrand Gold Rush
The Witwatersrand Gold Rush was a gold rush in 1886 that led to the establishment of Johannesburg, South Africa. It was part of the Mineral Revolution....

 in South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...

, and the Klondike
Klondike Gold Rush
The Klondike Gold Rush, also called the Yukon Gold Rush, the Alaska Gold Rush and the Last Great Gold Rush, was an attempt by an estimated 100,000 people to travel to the Klondike region the Yukon in north-western Canada between 1897 and 1899 in the hope of successfully prospecting for gold...

 in Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

.

Because of its historically high value, much of the gold mined throughout history is still in circulation in one form or another.

Occurrence


Gold's atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...

 of 79 makes it one of the higher atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...

 elements which occur naturally. Like all elements with atomic numbers larger than iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

, gold is thought to have been formed from a supernova nucleosynthesis
Supernova nucleosynthesis
Supernova nucleosynthesis is the production of new chemical elements inside supernovae. It occurs primarily due to explosive nucleosynthesis during explosive oxygen burning and silicon burning...

 process. Their explosions scattered metal-containing dusts (including heavy elements like gold) into the region of space in which they later condensed into our solar system
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...

 and the Earth. Because the Earth was molten when it was just formed, almost all of the gold present on Earth sank into the core. Most of the gold that is present today in the Earth's crust and mantle was delivered to Earth by asteroid impacts during the late heavy bombardment
Late Heavy Bombardment
The Late Heavy Bombardment is a period of time approximately 4.1 to 3.8 billion years ago during which a large number of impact craters are believed to have formed on the Moon, and by inference on Earth, Mercury, Venus, and Mars as well...

.

On Earth, whenever elemental gold occurs, it appears most often as a metal solid solution
Solid solution
A solid solution is a solid-state solution of one or more solutes in a solvent. Such a mixture is considered a solution rather than a compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single homogeneous phase...

 of gold with silver, i.e. a gold silver alloy. Such alloys usually have a silver content of 8–10%. Electrum
Electrum
Electrum is a naturally occurring alloy of gold and silver, with trace amounts of copper and other metals. It has also been produced artificially. The ancient Greeks called it 'gold' or 'white gold', as opposed to 'refined gold'. Its color ranges from pale to bright yellow, depending on the...

 is elemental gold with more than 20% silver. Electrum's color runs from golden-silvery to silvery, dependent upon the silver content. The more silver, the lower the specific gravity
Specific gravity
Specific gravity is the ratio of the density of a substance to the density of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for...

.
Gold is found in ore
Ore
An ore is a type of rock that contains minerals with important elements including metals. The ores are extracted through mining; these are then refined to extract the valuable element....

s made up of rock with very small or microscopic particles of gold. This gold ore is often found together with quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...

 or sulfide mineral
Sulfide mineral
The sulfide minerals are a class of minerals containing sulfide as the major anion. Some sulfide minerals are economically important as metal ores. The sulfide class also includes the selenides, the tellurides, the arsenides, the antimonides, the bismuthinides, the sulfarsenides and the sulfosalts...

s such as Fool's Gold, which is a pyrite
Pyrite
The mineral pyrite, or iron pyrite, is an iron sulfide with the formula FeS2. This mineral's metallic luster and pale-to-normal, brass-yellow hue have earned it the nickname fool's gold because of its resemblance to gold...

. These are called lode
Lode
In geology, a lode is a deposit of metalliferous ore that fills or is embedded in a fissure in a rock formation or a vein of ore that is deposited or embedded between layers of rock....

 deposits. Native gold is also found in the form of free flakes, grains or larger nugget
Gold nugget
A gold nugget is a naturally occurring piece of native gold. Watercourses often concentrate and grow the nuggets. Nuggets are recovered by placer mining, but they are also found in residual deposits where the gold-bearing veins or lodes are weathered...

s that have been eroded from rocks and end up in alluvial deposits (called placer deposit
Placer deposit
In geology, a placer deposit or placer is an accumulation of valuable minerals formed by gravity separation during sedimentary processes. The name is from the Spanish word placer, meaning "alluvial sand". Placer mining is an important source of gold, and was the main technique used in the early...

s). Such free gold is always richer at the surface of gold-bearing veins owing to the oxidation of accompanying minerals followed by weathering, and washing of the dust into streams and rivers, where it collects and can be welded by water action to form nugget
Gold nugget
A gold nugget is a naturally occurring piece of native gold. Watercourses often concentrate and grow the nuggets. Nuggets are recovered by placer mining, but they are also found in residual deposits where the gold-bearing veins or lodes are weathered...

s.

Gold sometimes occurs combined with tellurium as the mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...

s calaverite
Calaverite
Calaverite, or gold telluride, is an uncommon telluride of gold, a metallic mineral with the chemical formula AuTe2, with approximately 3% of the gold replaced by silver. It was first discovered in Calaveras County, California in 1861, and was named for the county in 1868.The mineral often has a...

, krennerite
Krennerite
Krennerite is an orthorhombic gold telluride mineral which can contain a relatively small amount of silver in the structure. The formula is AuTe2 varying to Te2. Both of the chemically similar gold-silver tellurides, calaverite and sylvanite are in the monoclinic crystal system, whereas krennerite...

, nagyagite
Nagyagite
Nagyagite is a rare sulfide mineral with known occurrence associated with gold ores. Nagyagite crystals are opaque, monoclinic and dark grey to black coloured....

, petzite
Petzite
The mineral petzite, Ag3AuTe2, is a soft, steel-gray telluride mineral generally deposited by hydrothermal activity. It forms isometric crystals, and is usually associated with rare tellurium and gold minerals, often with silver, mercury, and copper....

 and sylvanite
Sylvanite
Sylvanite or silver gold telluride, Te2, is the most common telluride of gold.-Properties:The gold:silver ratio varies from 3:1 to 1:1. It is a metallic mineral with a color that ranges from a steely gray to almost white. It is closely related to calaverite, which is more purely gold telluride with...

, and as the rare bismuthide maldonite (Au2Bi) and antimonide aurostibite
Aurostibite
Aurostibite is an isometric gold antimonide mineral which is a member of the pyrite group. Aurostibite was discovered in 1952 and can be found in hydrothermal gold-quartz veins, in sulfur-deficient environments that contain other antimony minerals. The mineral can be found in Yellowknife in the...

 (AuSb2). Gold also occurs in rare alloys with copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

, lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

, and mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

: the minerals auricupride
Auricupride
Auricupride is a natural alloy that combines copper and gold. Its chemical formula is Cu3Au. The alloy crystallizes in the Cubic crystal system and occurs as malleable grains or platey masses. It is an opaque yellow with a reddish tint. It has a hardness of 3.5 and a specific gravity of 11.5.A...

 (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.

The world's ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

s contain gold. Measured concentrations of gold in the Atlantic and Northeast Pacific are 50–150 fmol/L or 10–30 parts per quadrillion (about 10–30 g/km3). In general, Au concentrations for Atlantic and Pacific samples are the same (~50 fmol/L) but less certain. Mediterranean deep waters contain higher concentrations of Au (100–150 fmol/L) attributed to wind-blown dust and/or rivers. At 10 parts per quadrillion the Earth's oceans would hold 15,000 tons 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 so far they have all been either mistaken or acted in an intentional deception. A so-called reverend, Prescott Jernegan ran a gold-from-seawater swindle in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 in the 1890s. A British fraudster ran the same scam in England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

 in the early 1900s. Fritz Haber
Fritz Haber
Fritz Haber was a German chemist, who received the Nobel Prize in Chemistry in 1918 for his development for synthesizing ammonia, important for fertilizers and explosives. Haber, along with Max Born, proposed the Born–Haber cycle as a method for evaluating the lattice energy of an ionic solid...

 (the German inventor of the Haber process
Haber process
The Haber process, also called the Haber–Bosch process, is the nitrogen fixation reaction of nitrogen gas and hydrogen gas, over an enriched iron or ruthenium catalyst, which is used to industrially produce ammonia....

) did research on the extraction of gold from sea water in an effort to help pay Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

's reparations following World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

. 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 the extraction would not be possible and he stopped the project. No commercially viable mechanism for performing gold extraction from sea water has yet been identified. Gold synthesis is not economically viable and is unlikely to become so in the foreseeable future.


Production




Gold extraction
Gold extraction
Gold extraction or recovery from its ores may require a combination of comminution, mineral processing, hydrometallurgical, and pyrometallurgical processes to be performed on the ore....

 is most economical in large, easily mined deposits. Ore grades as little as 0.5 mg/kg (0.5 parts per million, ppm) can be economical. Typical ore grades in open-pit
Open-pit mining
Open-pit mining or opencast mining refers to a method of extracting rock or minerals from the earth by their removal from an open pit or borrow....

 mines are 1–5 mg/kg (1–5 ppm); ore grades in underground or hard rock mines are usually at least 3 mg/kg (3 ppm). Because ore grades of 30 mg/kg (30 ppm) are usually needed before gold is visible to the naked eye, in most gold mines the gold is invisible.

Since the 1880s, South Africa has been the source for a large proportion of the world's gold supply, with about 50% of all gold ever produced having come from South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...

. Production in 1970 accounted for 79% of the world supply, producing about 1,480 tonne
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...

s. 2008 production was 2,260 tonnes. In 2007 China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

 (with 276 tonnes) overtook South Africa as the world's largest gold producer, the first time since 1905 that South Africa has not been the largest.

The city of Johannesburg
Johannesburg
Johannesburg also known as Jozi, Jo'burg or Egoli, is the largest city in South Africa, by population. Johannesburg is the provincial capital of Gauteng, the wealthiest province in South Africa, having the largest economy of any metropolitan region in Sub-Saharan Africa...

 located in South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...

 was founded as a result of the Witwatersrand Gold Rush
Witwatersrand Gold Rush
The Witwatersrand Gold Rush was a gold rush in 1886 that led to the establishment of Johannesburg, South Africa. It was part of the Mineral Revolution....

 which resulted in the discovery of some of the largest gold deposits the world has ever seen. Gold fields located within the basin in the Free State
Free State
The Free State is a province of South Africa. Its capital is Bloemfontein, which is also South Africa's judicial capital. Its historical origins lie in the Orange Free State Boer republic and later Orange Free State Province. The current borders of the province date from 1994 when the Bantustans...

 and Gauteng
Gauteng
Gauteng is one of the nine provinces of South Africa. It was formed from part of the old Transvaal Province after South Africa's first all-race elections on 27 April 1994...

 provinces are extensive in strike and dip
Strike and dip
Strike and dip refer to the orientation or attitude of a geologic feature. The strike line of a bed, fault, or other planar feature is a line representing the intersection of that feature with a horizontal plane. On a geologic map, this is represented with a short straight line segment oriented...

 requiring some of the world's deepest mines, with the Savuka and TauTona
TauTona
The TauTona Mine or Western Deep No.3 Shaft, is a gold mine in South Africa. At some deep it is currently home to the world's deepest mining operations.-Overview:...

 mines being currently the world's deepest gold mine at 3,777 m. The Second Boer War
Second Boer War
The Second Boer War was fought from 11 October 1899 until 31 May 1902 between the British Empire and the Afrikaans-speaking Dutch settlers of two independent Boer republics, the South African Republic and the Orange Free State...

 of 1899–1901 between the British Empire
British Empire
The British Empire comprised the dominions, colonies, protectorates, mandates and other territories ruled or administered by the United Kingdom. It originated with the overseas colonies and trading posts established by England in the late 16th and early 17th centuries. At its height, it was the...

 and the Afrikaner
Afrikaner
Afrikaners are an ethnic group in Southern Africa descended from almost equal numbers of Dutch, French and German settlers whose native tongue is Afrikaans: a Germanic language which derives primarily from 17th century Dutch, and a variety of other languages.-Related ethno-linguistic groups:The...

 Boer
Boer
Boer is the Dutch and Afrikaans word for farmer, which came to denote the descendants of the Dutch-speaking settlers of the eastern Cape frontier in Southern Africa during the 18th century, as well as those who left the Cape Colony during the 19th century to settle in the Orange Free State,...

s was at least partly over the rights of miners and possession of the gold wealth in South Africa.

Other major producers are the United States, Australia, Russia and Peru
Peru
Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....

. Mines in South Dakota
South Dakota
South Dakota is a state located in the Midwestern region of the United States. It is named after the Lakota and Dakota Sioux American Indian tribes. Once a part of Dakota Territory, South Dakota became a state on November 2, 1889. The state has an area of and an estimated population of just over...

 and Nevada
Nevada
Nevada is a state in the western, mountain west, and southwestern regions of the United States. With an area of and a population of about 2.7 million, it is the 7th-largest and 35th-most populous state. Over two-thirds of Nevada's people live in the Las Vegas metropolitan area, which contains its...

 supply two-thirds of gold used in the United States. In South America, the controversial project Pascua Lama
Pascua Lama
Pascua-Lama is an open pit mining project of gold, silver, copper and other minerals. Pascua Lama is located in the Andes mountains, south of Atacama, straddling the border between Chile and Argentina at an altitude of over 4,500 metres. Toronto-based Barrick Gold, the world's largest gold mining...

 aims at exploitation of rich fields in the high mountains of Atacama Desert
Atacama Desert
The Atacama Desert is a plateau in South America, covering a strip of land on the Pacific coast, west of the Andes mountains. It is, according to NASA, National Geographic and many other publications, the driest desert in the world...

, at the border between Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...

 and Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...

. Today about one-quarter of the world gold output is estimated to originate from artisanal or small scale mining.

After initial production, gold is often subsequently refined industrially by the Wohlwill process
Wohlwill process
The Wohlwill process is an industrial-scale chemical procedure used to refine gold to the highest degree of purity . The process was invented in 1874 by Emil Wohlwill. This electrochemical process involves using a cast dore ingot, often called a Doré bar, of 95%+ gold to serve as an anode...

 which is based on electrolysis
Electrolysis
In chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...

 or by the Miller process
Miller process
The Miller process is an industrial-scale chemical procedure used to refine gold to a high degree of purity . It was invented by Francis Bowyer Miller. This chemical process involves blowing a stream of pure chlorine gas over and through a crucible filled with molten, but impure, gold...

, 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
Cupellation
Cupellation is a metallurgical process in which ores or alloyed metals are treated under high temperatures and carefully controlled operations in order to separate noble metals, like gold and silver, from base metals like lead, copper, zinc, arsenic, antimony or bismuth, that might be present in...

, or refining methods based on the dissolution of gold in aqua regia.

At the end of 2009, it was estimated that all the gold ever mined totaled 165,000 tonnes. This can be represented by a cube with an edge length of about 20.28 meters. At $1,600 per ounce, 165,000 tons of gold would have a value of $8.8 trillion.

The average gold mining and extraction costs were about US$317/oz in 2007, but these can vary widely depending on mining type and ore quality; global mine production amounted to 2,471.1 tonnes.

Most of the gold used in manufactured goods, jewelry, and works of art is eventually recovered and recycled. Some gold used in spacecraft and electronic equipment cannot be profitably recovered, but it is generally used in these applications in the form of extremely thin layers or extremely fine wires so that the total quantity used (and lost) is small compared to the total amount of gold produced and stockpiled. Thus there is little true consumption of new gold in the economic sense; the stock of gold remains essentially constant (at least in the modern world) while ownership shifts from one party to another. One estimate is that 85% of all the gold ever mined is still available in the world's easily recoverable stocks, with 15% having been lost, or used in non-recyclable industrial uses.

Consumption


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

India is the world's largest single consumer of gold, as Indians buy about 25% of the world's gold, purchasing approximately 800 tonnes of gold every year, mostly for jewelry. India is also the largest importer of gold; in 2008, India imported around 400 tonnes of gold.
Gold jewellery consumption by country (in Tonnes).
Country 2010 2009 % Change
 India 745.70 442.37 +69
Greater China
Greater China
Greater China is a term used to refer to mainland China, Hong Kong, Macau and Taiwan. As a "phrase of the moment", the precise meaning is not entirely clear, and people may use it for only the commercial ties, only the cultural actions, or even as a euphemism for the Two Chinas, while others may...

 
428.00 376.96 +14
 United States 128.61 150.28 -14
 Turkey 74.07 75.16 -1
 Saudi Arabia 72.95 77.75 -6
 Russia 67.50 60.12 +12
 United Arab Emirates 63.37 67.60 -6
 Egypt 53.43 56.68 -6
 Indonesia 32.75 41.00 -20
 United Kingdom 27.35 31.75 -14
Other Gulf Countries 21.97 24.10 -10
 Japan 18.50 21.85 -15
 South Korea 15.87 18.83 -16
 Vietnam 14.36 15.08 -5
 Thailand 6.28 7.33 -14
Total 1805.60 1508.70 +20
Other Countries 254.0 251.6 +1
World Total 2059.6 1760.3 +17

Chemistry


Although gold is a noble metal
Noble metal
Noble metals are metals that are resistant to corrosion and oxidation in moist air, unlike most base metals. They tend to be precious, often due to their rarity in the Earth's crust...

, it forms many and diverse compounds. The oxidation state
Oxidation state
In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...

 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 ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...

s such as thioether
Thioether
A thioether is a functional group in organosulfur chemistry with the connectivity C-S-C as shown on right. Like many other sulfur-containing compounds, volatile thioethers have foul odors. A thioether is similar to an ether except that it contains a sulfur atom in place of the oxygen...

s, thiolates, and tertiary phosphine
Phosphine
Phosphine is the compound with the chemical formula PH3. It is a colorless, flammable, toxic gas. Pure phosphine is odourless, but technical grade samples have a highly unpleasant odor like garlic or rotting fish, due to the presence of substituted phosphine and diphosphine...

s. Au(I) compounds are typically linear. A good example is Au(CN)2
Gold cyanidation
Gold cyanidation is a metallurgical technique for extracting gold from low-grade ore by converting the gold to a water soluble coordination complex. It is the most commonly used process for gold extraction...

, which is the soluble form of gold encountered in mining. Curiously, aurous complexes of water are rare. The binary gold halide
Gold halide
- Monohalides :AuCl, AuBr, and AuI are all crystalline solids with a structure containing alternating linear chains: ..-X-Au-X-Au-X-Au-X-... The X-Au-X angle is 180°.The monomeric AuF molecule has been detected in the gas phase.- Trihalides :...

s, such as AuCl, form zigzag polymeric chains, again featuring linear coordination at Au. Most drugs based on gold are Au(I) derivatives.

Au(III) (auric) is a common oxidation state, and is illustrated by gold(III) chloride
Gold(III) chloride
Gold chloride, traditionally called auric chloride, is a chemical compound of gold and chlorine. With the molecular formula Au2Cl6, the name gold trichloride is a simplification, referring to the empirical formula. The Roman numerals in the name indicate that the gold has an oxidation state of +3,...

, Au2Cl6. The gold atom centers in Au(III) complexes, like other d8 compounds, are typically square planar
Square planar
The square planar molecular geometry in chemistry describes the stereochemistry that is adopted by certain chemical compounds...

, with chemical bond
Chemical bond
A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...

s that have both covalent and ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

ic character.

Aqua regia
Aqua regia
Aqua regia or aqua regis is a highly corrosive mixture of acids, fuming yellow or red solution, also called nitro-hydrochloric acid. The mixture is formed by freshly mixing concentrated nitric acid and hydrochloric acid, usually in a volume ratio of 1:3, respectively...

, a 1:3 mixture of nitric acid
Nitric acid
Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...

 and hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....

, dissolves gold. 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
Chloroauric acid
Chloroauric acid is a inorganic compound with the formula HAuCl4. This pale yellow compound is a common precursor to gold in a variety of purposes. The term chloroauric acid is also sometimes used to describe other gold chlorides....

, thereby enabling further oxidation.

Some free halogen
Halogen
The halogens or halogen elements are a series of nonmetal elements from Group 17 IUPAC Style of the periodic table, comprising fluorine , chlorine , bromine , iodine , and astatine...

s react with gold. Gold also reacts in alkaline solutions of potassium cyanide
Potassium cyanide
Potassium cyanide is an inorganic compound with the formula KCN. This colorless crystalline compound, similar in appearance to sugar, is highly soluble in water. Most KCN is used in gold mining, organic synthesis, and electroplating. Smaller applications include jewelry for chemical gilding and...

. With mercury, it forms an amalgam
Amalgam (chemistry)
An amalgam is a substance formed by the reaction of mercury with another metal. Almost all metals can form amalgams with mercury, notable exceptions being iron and platinum. Silver-mercury amalgams are important in dentistry, and gold-mercury amalgam is used in the extraction of gold from ore.The...

.

Less common oxidation states


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

The −1 oxidation state occurs in compounds containing the Au anion, called aurides. Caesium auride
Caesium auride
Caesium auride is an ionic compound containing the unusual Au− ion. It is obtained by heating a stoichiometric mixture of cesium and gold; the two metallic-yellow liquids react to give a clear product...

 (CsAu), for example, crystallizes in the caesium chloride
Caesium chloride
Caesium chloride is the inorganic compound with the formula CsCl. This colorless solid is an important source of caesium ions in a variety of applications. Its crystal structure forms a major structural type where each caesium ion is coordinated by 8 chlorine ions...

 motif. Other aurides include those of Rb
Rubidium
Rubidium is a chemical element with the symbol Rb and atomic number 37. Rubidium is a soft, silvery-white metallic element of the alkali metal group. Its atomic mass is 85.4678. Elemental rubidium is highly reactive, with properties similar to those of other elements in group 1, such as very rapid...

+, K
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...

+, and tetramethylammonium (CH3)4N+. Gold has the highest Pauling electronegativity
Electronegativity
Electronegativity, symbol χ , is a chemical property that describes the tendency of an atom or a functional group to attract electrons towards itself. An atom's electronegativity is affected by both its atomic number and the distance that its valence electrons reside from the charged nucleus...

 of any metal, with a value of 2.54, making the auride anion relatively stable.

Gold(II) compounds are usually diamagnetic with Au–Au bonds such as [Au(CH2)2P(C6H5)2]2Cl2. The evaporation of a solution of in concentrated produces red crystals of gold(II) sulfate, Au2(SO4)2. Originally thought to be a mixed-valence compound, it has been shown to contain cations. A noteworthy, legitimate gold(II) complex is the tetraxenonogold(II) cation, which contains xenon
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced or . A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...

 as a ligand, found in [AuXe4](Sb2F11)2.

Gold pentafluoride and its derivative anion, , is the sole example of gold(V), the highest verified oxidation state.

Some gold compounds exhibit aurophilic bonding
Aurophilicity
In chemistry, aurophilicity refers to the tendency of gold complexes to aggregate via formation of weak gold-gold bonds.-Overview:The phenomenon of aurophilicity is most commonly observed crystallographically for Au compounds. The aurophilic bond has a length of about 3.0 Å and a strength of about...

, which describes the tendency of gold ions to interact at distances that are too long to be a conventional Au–Au bond but shorter that van der Waals bonding
Van der Waals force
In physical chemistry, the van der Waals force , named after Dutch scientist Johannes Diderik van der Waals, is the sum of the attractive or repulsive forces between molecules other than those due to covalent bonds or to the electrostatic interaction of ions with one another or with neutral...

. The interaction is estimated to be comparable in strength to that of a hydrogen bond
Hydrogen bond
A hydrogen bond is the attractive interaction of a hydrogen atom with an electronegative atom, such as nitrogen, oxygen or fluorine, that comes from another molecule or chemical group. The hydrogen must be covalently bonded to another electronegative atom to create the bond...

.

Mixed valence compounds


Well-defined cluster compounds are numerous. In such cases, gold has a fractional oxidation state. A representative example is the octahedral species {Au(P(C6H5)3
Triphenylphosphine
Triphenylphosphine is a common organophosphorus compound with the formula P3 - often abbreviated to PPh3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists as relatively air stable, colorless crystals at room temperature...

)}62+. Gold chalcogenides
Gold chalcogenides
Gold chalcogenides are compounds formed between gold and one of the chalcogens, elements from group 16 of the periodic table: oxygen, sulfur, selenium, or tellurium....

, such as gold sulfide, feature equal amounts of Au(I) and Au(III).

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
Gold leaf
right|thumb|250px|[[Burnishing]] gold leaf with an [[agate]] stone tool, during the water gilding processGold leaf is gold that has been hammered into extremely thin sheets and is often used for gilding. Gold leaf is available in a wide variety of karats and shades...

. Metallic gold is also a component of the alcoholic drinks Goldschläger
Goldschläger
Goldschläger is a Swiss cinnamon schnapps , a liqueur with very thin, yet visible flakes of gold leaf floating in it...

, Gold Strike
Gold Strike (drink)
Goldstrike: a popular shooter with cinnamon flavor and 24-karat gold snippets and an individual drinking method: “Shake, Shoot and Strike” and produced by Lucas Bols. It is a clear liquid, that tastes like cinnamon candy....

, and Goldwasser
Goldwasser
Danziger Goldwasser ), with Goldwasser as the registered tradename, is a strong root and herbal liqueur which has been produced since at least 1598 in Danzig ....

. Metallic gold is approved as a food additive
Food additive
Food additives are substances added to food to preserve flavor or enhance its taste and appearance.Some additives have been used for centuries; for example, preserving food by pickling , salting, as with bacon, preserving sweets or using sulfur dioxide as in some wines...

 in the EU (E175
E number
E numbers are number codes for food additives that have been assessed for use within the European Union . They are commonly found on food labels throughout the European Union. Safety assessment and approval are the responsibility of the European Food Safety Authority...

 in the Codex Alimentarius
Codex Alimentarius
The Codex Alimentarius is a collection of internationally recognized standards, codes of practice, guidelines and other recommendations relating to foods, food production and food safety. Its name derives from the Codex Alimentarius Austriacus...

). Although 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
Gold salts
Gold salts describe ionic chemical compounds of gold. The term, which is a misnomer, has evolved into a synonym for the gold compounds used in medicine...

) such as gold chloride
Gold(I,III) chloride
Gold chloride is a black solid with chemical formula Au4Cl8 that contains gold in two different oxidation states - +1 and +3. It is a photosensitive solid and should be kept away from light and stored in dark-coloured containers.- References :...

 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
Chelation therapy
Chelation therapy is the administration of chelating agents to remove heavy metals from the body. For the most common forms of heavy metal intoxication—those involving lead, arsenic or mercury—the standard of care in the United States dictates the use of dimercaptosuccinic acid...

 with an agent such as Dimercaprol
Dimercaprol
Dimercaprol or British anti-Lewisite , is a compound developed by British biochemists at Oxford University during World War II. It was developed secretly as an antidote for lewisite, the now-obsolete arsenic-based chemical warfare agent. Today, it is used medically in treatment of arsenic,...

.

Gold metal was voted Allergen of the Year
Allergen of the Year
Allergen of the Year is an annual 'award' of dubious distinction voted upon by the American Contact Dermatitis Society. It is "designed to draw attention to allergens that are very common and/or under-recognized and merit more attention because they are causing significant allergic contact...

 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
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...

.

Price



Like other precious metals, gold is measured by troy weight
Troy weight
Troy weight is a system of units of mass customarily used for precious metals, gemstones, and black powder.There are 12 troy ounces per troy pound, rather than the 16 ounces per pound found in the more common avoirdupois system. The troy ounce is 480 grains, compared with the avoirdupois ounce,...

 and by grams. When it is alloyed with other metals the term carat
Carat (purity)
The karat or carat is a unit of purity for gold alloys.- Measure :Karat purity is measured as 24 times the purity by mass:where...

or karat is used to indicate the purity of gold present, with 24 carats being pure gold and lower ratings proportionally less. The purity of a gold bar
Gold bar
A gold bar is a quantity of refined metallic gold of any shape that is made by a bar producer meeting standard conditions of manufacture, labeling, and record keeping....

 or coin can also be expressed as a decimal figure ranging from 0 to 1, known as the millesimal fineness
Millesimal fineness
Millesimal fineness is a system of denoting the purity of platinum, gold and silver alloys by parts per thousand of pure metal by mass in the alloy. For example, an alloy containing 75% gold is denoted as "750". Many European countries use decimal hallmark stamps Millesimal fineness is a system of...

, such as 0.995 being very pure.

The price of gold is determined through trading in the gold and derivatives
Derivative (finance)
A derivative instrument is a contract between two parties that specifies conditions—in particular, dates and the resulting values of the underlying variables—under which payments, or payoffs, are to be made between the parties.Under U.S...

 markets, but a procedure known as the Gold Fixing
Gold Fixing
The London gold fixing or gold fix is the procedure by which the price of gold is determined twice each business day on the London market by the five members of The London Gold Market Fixing Ltd, on the premises of N M Rothschild & Sons...

 in London
London
London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

, 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.

Historically gold coinage
Mint (coin)
A mint is an industrial facility which manufactures coins for currency.The history of mints correlates closely with the history of coins. One difference is that the history of the mint is usually closely tied to the political situation of an era...

 was widely used as currency; when paper money
Paper Money
Paper Money is the second album by the band Montrose. It was released in 1974 and was the band's last album to feature Sammy Hagar as lead vocalist.-History:...

 was introduced, it typically was a receipt
Receipt
A receipt is a written acknowledgment that a specified article or sum of money has been received as an exchange for goods or services. The receipt is evidence of purchase of the property or service obtained in the exchange.-Printed:...

 redeemable for gold coin or bullion. In a monetary system known as the gold standard
Gold standard
The gold standard is a monetary system in which the standard economic unit of account is a fixed mass of gold. There are distinct kinds of gold standard...

, a certain weight
Weight
In science and engineering, the weight of an object is the force on the object due to gravity. Its magnitude , often denoted by an italic letter W, is the product of the mass m of the object and the magnitude of the local gravitational acceleration g; thus:...

 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
Troy ounce
The troy ounce is a unit of imperial measure. In the present day it is most commonly used to gauge the weight of precious metals. One troy ounce is nowadays defined as exactly 0.0311034768 kg = 31.1034768 g. There are approximately 32.1507466 troy oz in 1 kg...

 was equal to $20.67 ($664.56/kg), but in 1934 the dollar was devalued to $35.00 per troy ounce ($1125.27/kg). 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
Devaluation
Devaluation is a reduction in the value of a currency with respect to those goods, services or other monetary units with which that currency can be exchanged....

 against increased gold demand.


On March 17, 1968, economic circumstances 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. Central bank
Central bank
A central bank, reserve bank, or monetary authority is a public institution that usually issues the currency, regulates the money supply, and controls the interest rates in a country. Central banks often also oversee the commercial banking system of their respective countries...

s still hold historical gold reserves
Official gold reserves
A gold reserve is the gold held by a central bank or nation intended as a store of value and as a guarantee to redeem promises to pay depositors, note holders , or trading peers, or to secure a currency....

 as a store of value
Store of value
A recognized form of exchange can be a form of money or currency, a commodity like gold, or financial capital. To act as a store of value, these forms must be able to be saved and retrieved at a later time, and be predictably useful when retrieved....

 although the level has generally been declining. The largest gold depository in the world is that of the U.S. Federal Reserve Bank
Federal Reserve System
The Federal Reserve System is the central banking system of the United States. It was created on December 23, 1913 with the enactment of the Federal Reserve Act, largely in response to a series of financial panics, particularly a severe panic in 1907...

 in New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...

, which holds about 3% of the gold ever mined, as does the similarly laden U.S. Bullion Depository
United States Bullion Depository
The United States Bullion Depository, often known as Fort Knox, is a fortified vault building located adjacent to Fort Knox, Kentucky, used to store a large portion of United States official gold reserves and occasionally other precious items belonging or entrusted to the federal government.The...

 at Fort Knox
Fort Knox
Fort Knox is a United States Army post in Kentucky south of Louisville and north of Elizabethtown. The base covers parts of Bullitt, Hardin, and Meade counties. It currently holds the Army Human Resources Center of Excellence to include the Army Human Resources Command, United States Army Cadet...

.
In 2005 the World Gold Council
World Gold Council
The World Gold Council is a non-profit association of the world's leading gold mining companies, established in 1987 to promote the use of gold. It aims to stimulate demand for gold from industry, consumers, and investors. The Council's Chief Executive Officer is Aram Shishmanian, former head of...

 estimated total global gold supply to be 3,859 tonnes and demand to be 3,754 tonnes, giving a surplus of 105 tonnes.

Since 1968 the price of gold has ranged widely, from a high of $850/oz ($27,300/kg) on January 21, 1980, to a low of $252.90/oz ($8,131/kg) on June 21, 1999 (London Gold Fixing). The period from 1999 to 2001 marked the "Brown Bottom
Brown Bottom
The sale of UK gold reserves was a policy pursued by HM Treasury over the period between 1999 and 2002, when gold prices were at their lowest in 20 years, following an extended bear market...

" after a 20-year bear market. Prices increased rapidly from 1991, but the 1980 high was not exceeded until January 3, 2008 when a new maximum of $865.35 per troy ounce
Troy weight
Troy weight is a system of units of mass customarily used for precious metals, gemstones, and black powder.There are 12 troy ounces per troy pound, rather than the 16 ounces per pound found in the more common avoirdupois system. The troy ounce is 480 grains, compared with the avoirdupois ounce,...

 was set. Another record price was set on March 17, 2008 at $1023.50/oz ($32,900/kg). In late 2009, gold markets experienced renewed momentum upwards due to increased demand and a weakening US dollar. On December 2, 2009, Gold passed the important barrier of US$1200 per ounce to close at $1215. 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 March 1, 2011, gold hit a new all-time high of $1432.57, based on investor
Gold as an investment
Of all the precious metals, gold is the most popular as an investment. Investors generally buy gold as a hedge or harbor against economic, political, or social fiat currency crises...

 concerns regarding ongoing unrest
2010–2011 Middle East and North Africa protests
The Arab Spring , otherwise known as the Arab Awakening, is a revolutionary wave of demonstrations and protests occurring in the Arab world that began on Saturday, 18 December 2010...

 in North Africa
North Africa
North Africa or Northern Africa is the northernmost region of the African continent, linked by the Sahara to Sub-Saharan Africa. Geopolitically, the United Nations definition of Northern Africa includes eight countries or territories; Algeria, Egypt, Libya, Morocco, South Sudan, Sudan, Tunisia, and...

 as well as in the Middle East
Middle East
The Middle East is a region that encompasses Western Asia and Northern Africa. It is often used as a synonym for Near East, in opposition to Far East...

.

Since April 2001 the gold price has more than quintupled in value against the US dollar, hitting a new all-time high of $1,913.50 on August 23, 2011, prompting speculation that this long secular bear market has ended and a bull market has returned.

Symbolism



Gold has been highly valued in many societies throughout the ages. In keeping with this it has often had a strongly positive symbolic meaning closely connected to the values held in the highest esteem in the society in question. Gold may symbolize power, strength, wealth, warmth, happiness, love, hope, optimism, intelligence, justice, balance, perfection, summer, harvest and the sun.

Great human achievements are frequently rewarded with gold, in the form of gold medal
Gold medal
A gold medal is typically the medal awarded for highest achievement in a non-military field. Its name derives from the use of at least a fraction of gold in form of plating or alloying in its manufacture...

s, golden trophies
Trophy
A trophy is a reward for a specific achievement, and serves as recognition or evidence of merit. Trophies are most often awarded for sporting events, from youth sports to professional level athletics...

 and other decorations. Winners of athletic events and other graded competitions are usually awarded a gold medal (e.g., the Olympic Games
Olympic Games
The Olympic Games is a major international event featuring summer and winter sports, in which thousands of athletes participate in a variety of competitions. The Olympic Games have come to be regarded as the world’s foremost sports competition where more than 200 nations participate...

). Many awards such as the Nobel Prize
Nobel Prize
The Nobel Prizes are annual international awards bestowed by Scandinavian committees in recognition of cultural and scientific advances. The will of the Swedish chemist Alfred Nobel, the inventor of dynamite, established the prizes in 1895...

 are made from gold as well. Other award statues and prizes are depicted in gold or are gold plated (such as the Academy Awards
Academy Awards
An Academy Award, also known as an Oscar, is an accolade bestowed by the American Academy of Motion Picture Arts and Sciences to recognize excellence of professionals in the film industry, including directors, actors, and writers...

, the Golden Globe Awards, the Emmy Awards, the Palme d'Or
Palme d'Or
The Palme d'Or is the highest prize awarded at the Cannes Film Festival and is presented to the director of the best feature film of the official competition. It was introduced in 1955 by the organising committee. From 1939 to 1954, the highest prize was the Grand Prix du Festival International du...

, and the British Academy Film Awards
British Academy Film Awards
The British Academy Film Awards are presented in an annual award show hosted by the British Academy of Film and Television Arts . It is the British counterpart of the Oscars. As of 2008, it has taken place in the Royal Opera House, having taken over from the flagship Odeon cinema on Leicester Square...

).

Aristotle
Aristotle
Aristotle was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology...

 in his ethics
Aristotelian ethics
Ethics as a subject begins with the works of Aristotle. In its original form, this subject is concerned with the question of virtue of character , or in other words having excellent and well-chosen habits. The acquisition of an excellent character is in turn aimed at living well and eudaimonia, a...

 used gold symbolism when referring to what is now commonly known as the "golden mean
Golden mean (philosophy)
In philosophy, especially that of Aristotle, the golden mean is the desirable middle between two extremes, one of excess and the other of deficiency. For example courage, a virtue, if taken to excess would manifest as recklessness and if deficient as cowardice....

". Similarly, gold is associated with perfect or divine principles, such as in the case of the "golden ratio
Golden ratio
In mathematics and the arts, two quantities are in the golden ratio if the ratio of the sum of the quantities to the larger quantity is equal to the ratio of the larger quantity to the smaller one. The golden ratio is an irrational mathematical constant, approximately 1.61803398874989...

".

Gold represents great value. Respected people are treated with the most valued rule, the "golden rule
Golden Rule
Golden Rule may refer to:*The Golden Rule in ethics, morality, history and religion, also known as the ethic of reciprocity*Golden Rule savings rate, in economics, the savings rate which maximizes consumption in the Solow growth model...

". A company may give its most valued customers "gold cards" or make them "gold members". We value moments of peace and therefore we say: "silence is golden". In Greek mythology there was the "golden fleece
Golden Fleece
In Greek mythology, the Golden Fleece is the fleece of the gold-haired winged ram, which can be procured in Colchis. It figures in the tale of Jason and his band of Argonauts, who set out on a quest by order of King Pelias for the fleece in order to place Jason rightfully on the throne of Iolcus...

".

Gold is further associated with the wisdom of aging and fruition. The fiftieth wedding anniversary
Wedding anniversary
-Official recognition:In the Commonwealth realms, one can receive a message from the monarch for 60th, 65th, and 70th wedding anniversaries, and any wedding anniversary after that...

 is golden. Our precious latter years are sometimes considered "golden years". The height of a civilization is referred to as a "golden age
Golden Age
The term Golden Age comes from Greek mythology and legend and refers to the first in a sequence of four or five Ages of Man, in which the Golden Age is first, followed in sequence, by the Silver, Bronze, and Iron Ages, and then the present, a period of decline...

".

In Christianity
Christianity
Christianity is a monotheistic religion based on the life and teachings of Jesus as presented in canonical gospels and other New Testament writings...

 gold has sometimes been associated with the extremities of utmost evil and the greatest sanctity. In the Book of Exodus, the Golden Calf
Golden calf
According to the Hebrew Bible, the golden calf was an idol made by Aaron to satisfy the Israelites during Moses' absence, when he went up to Mount Sinai...

 is a symbol of idolatry
Idolatry
Idolatry is a pejorative term for the worship of an idol, a physical object such as a cult image, as a god, or practices believed to verge on worship, such as giving undue honour and regard to created forms other than God. In all the Abrahamic religions idolatry is strongly forbidden, although...

. In the Book of Genesis, Abraham
Abraham
Abraham , whose birth name was Abram, is the eponym of the Abrahamic religions, among which are Judaism, Christianity and Islam...

 was said to be rich in gold and silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...

, and Moses was instructed to cover the Mercy Seat
Mercy seat
According to the Bible, the mercy seat was an object which rested upon the Ark of the Covenant, and was connected with the rituals of Yom Kippur; the term also appears in the Pauline Epistles, and has a significance in Christian theology...

 of the Ark of the Covenant
Ark of the Covenant
The Ark of the Covenant , also known as the Ark of the Testimony, is a chest described in Book of Exodus as solely containing the Tablets of Stone on which the Ten Commandments were inscribed...

 with pure gold. In Christian art the halos
Halo (religious iconography)
A halo is a ring of light that surrounds a person in art. They have been used in the iconography of many religions to indicate holy or sacred figures, and have at various periods also been used in images of rulers or heroes...

 of Christ
Christ
Christ is the English term for the Greek meaning "the anointed one". It is a translation of the Hebrew , usually transliterated into English as Messiah or Mashiach...

, Mary and the Christian saints are golden.

Medieval kings were inaugurated under the signs of sacred oil
Anointing
To anoint is to pour or smear with perfumed oil, milk, water, melted butter or other substances, a process employed ritually by many religions. People and things are anointed to symbolize the introduction of a sacramental or divine influence, a holy emanation, spirit, power or God...

 and a golden crown, the latter symbolizing the eternal shining light of heaven and thus a Christian king's divinely inspired authority. Wedding ring
Wedding ring
A wedding ring or wedding band is a metal ring indicating the wearer is married. Depending on the local culture, it is worn on the base of the right or the left ring finger. The custom of wearing such a ring has spread widely beyond its origin in Europe...

s have long been 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/or the sun and moon and the perfection the marriage signifies. In Orthodox Christianity
Eastern Orthodox Church
The Orthodox Church, officially called the Orthodox Catholic Church and commonly referred to as the Eastern Orthodox Church, is the second largest Christian denomination in the world, with an estimated 300 million adherents mainly in the countries of Belarus, Bulgaria, Cyprus, Georgia, Greece,...

, the wedded couple is adorned with a golden crown during the ceremony, an amalgamation of symbolic rites.

In popular culture gold holds many connotations but is most generally connected to terms such as good or great, such as in the phrases: "has a heart of gold", "that's golden!", "golden moment", "then you're golden!" and "golden boy". Gold also still holds its place as a symbol of wealth and through that, in many societies, success.

State emblem


In 1965, the California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

 Legislature designated gold "the State Mineral and mineralogical emblem."

In 1968, the Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...

 Legislature named gold "the official state mineral."

See also


  • Altai Mountains
  • Bulk leach extractable gold
    Bulk leach extractable gold
    Bulk Leach Extractable Gold, more commonly shortened to BLEG is a geochemical sampling/analysis tool used during exploration for gold. It was developed in the early 1980s to address concerns relating to the accurately measuring fine grained gold, and dealing with problems associated with sample...

  • Commodity fetishism
    Commodity fetishism
    In Marx's critique of political economy, commodity fetishism denotes the mystification of human relations said to arise out of the growth of market trade, when social relationships between people are expressed as, mediated by and transformed into, objectified relationships between things .The...

     (Marxist economic theory)
  • Digital gold currency
    Digital gold currency
    Digital gold currency is a form of electronic money based on ounces of gold. It is a kind of representative money, like a US paper gold certificate at the time that these were exchangeable for gold on demand. The typical unit of account for such currency is the gold gram or the troy ounce,...

  • Gold Anti-Trust Action Committee
    Gold Anti-Trust Action Committee
    The Gold Anti-Trust Action Committee is an organization dedicated to investigating and proving its allegation that the quantity of gold held and traded by the world's central banks, international bullion banks and futures exchanges is significantly overstated and that a scheme analogous to the...

  • Gold bubble
  • Gold fingerprinting
    Gold fingerprinting
    Gold fingerprinting is a method for identifying a particular item made of gold based on the impurities or trace elements it contains.- Method:...

  • Gold phosphine complex
  • Gold Prospectors Association of America
    Gold Prospectors Association of America
    The Gold Prospectors Association of America is an organization dedicated to finding and mining gold on a small or recreational scale. It has gold claims across America and members can work the claims for a yearly fee. The club is headquartered in Temecula, California. Most, if not all GPAA...

  • Mining in Roman Britain
    Mining in Roman Britain
    Mining was one of the most prosperous activities in Roman Britain. Britain was rich in resources such as copper, gold, iron, lead, salt, silver, and tin, materials in high demand in the Roman Empire. The abundance of mineral resources in the British Isles was probably one of the reasons for the...

  • Prospecting
    Prospecting
    Prospecting is the physical search for minerals, fossils, precious metals or mineral specimens, and is also known as fossicking.Prospecting is a small-scale form of mineral exploration which is an organised, large scale effort undertaken by mineral resource companies to find commercially viable ore...

  • Roman engineering
    Roman engineering
    Romans are famous for their advanced engineering accomplishments, although some of their own inventions were improvements on older ideas, concepts and inventions. Technology for bringing running water into cities was developed in the east, but transformed by the Romans into a technology...

  • Tumbaga
    Tumbaga
    Tumbaga was the name given by Spaniards to a non-specific alloy of gold and copper which they found in widespread use in pre-Columbian Mesoamerica and South America.-Composition and properties:...


External links