Difference between revisions of "Gold" - New World Encyclopedia

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'''Gold''' is a shiny yellow [[metal]] that has long been highly valued and regarded as a symbol for purity, permanence, and royalty. It occurs as [[gold nugget|nuggets]] or grains in rocks and [[alluvial deposit]]s and does not react with most chemicals.
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{{Elementbox_header | number=79 | symbol=Au | name=gold | left=[[platinum]] | right=[[mercury (element)|mercury]] | above=[[silver|Ag]] | below=[[roentgenium|Rg]] | color1=#ffc0c0 | color2=black }}
 
{{Elementbox_header | number=79 | symbol=Au | name=gold | left=[[platinum]] | right=[[mercury (element)|mercury]] | above=[[silver|Ag]] | below=[[roentgenium|Rg]] | color1=#ffc0c0 | color2=black }}
 
{{Elementbox_series | [[transition metal]]s }}
 
{{Elementbox_series | [[transition metal]]s }}
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{{Elementbox_isotopes_end}}
 
{{Elementbox_isotopes_end}}
 
{{Elementbox_footer | color1=#ffc0c0 | color2=black }}
 
{{Elementbox_footer | color1=#ffc0c0 | color2=black }}
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'''Gold''' (chemical symbol '''Au'''; atomic number 79) has long been valued as a [[metal|noble metal]] and a symbol of purity, durability, and royalty. Its attractive yellow shine, resistance to corrosion, and relative rarity have made it extremely appealing for use in jewelry, ornaments, and coinage. Kings have chosen to wear golden crowns, and couples have expressed their undying love with gold wedding rings. Yet the attractiveness of gold has also brought out the worst of human nature, as it has been an object of thieves and conquerors. In recent years, gold has been incorporated in a wide variety of products, including computers, communications hardware, aircraft, and spacecraft, and newer applications continue to be tested.
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{{toc}}
  
 
==History==
 
==History==
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Gold ([[Sanskrit]] ''jval'', [[Greek language|Greek]] χρυσος [''khrusos''], [[Latin]] ''aurum'' for "shining dawn", [[Anglo-Saxon language|Anglo-Saxon]] ''gold'', [[Chinese language|Chinese]] 金 [''jīn''],[[Japanese language|Japanese]] 金 [''kin'']) is a precious metal that has been known and highly valued since prehistoric times. Early peoples used it mainly for ornamentation and rituals. Gold is described in [[Egyptian hieroglyph]]s dating back to [[2600 B.C.E.]], and it is mentioned several times in the [[Hebrew scriptures]].
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[[Image:Krone Kaiser Rudolf II Kaisertum Österreich.jpg|thumb|left|Crown of the Austrian Empire]]
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Gold ([[Sanskrit]] ''jval'', [[Greek language|Greek]] χρυσος [''khrusos''], [[Latin]] ''aurum'' for "shining dawn," [[Anglo-Saxon language|Anglo-Saxon]] ''gold,'' [[Chinese language|Chinese]] 金 [''jīn''], [[Japanese language|Japanese]] 金 [''kin'']) is a [[chemical element]] and a precious [[metal]] that has been known and highly valued since prehistoric times. Early peoples used it mainly for ornamentation and rituals.
  
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[[Egypt]] and [[Nubia]] had the resources to make them major gold-producing areas for much of history. The southeast corner of the [[Black Sea]] was famed for its gold. Exploitation is said to date from the time of [[Midas]], and this gold was important in the establishment of what was probably the world's earliest coinage in [[Lydia]] between [[630s B.C.E.|643 and 630 B.C.E.]].
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Gold is described in [[Egyptian hieroglyph]]s dating back to 2600 <small>B.C.E.</small>, and it is mentioned several times in the [[Hebrew scriptures]]. Ancient [[Egypt]] and [[Nubia]] had the resources to make them major gold-producing areas. The tombs of the Egyptian [[pharaoh]]s were filled with items made of, or plated with, gold.
  
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The European exploration of the Americas was fueled in no small part by reports of the gold ornaments displayed in great profusion by [[Indigenous peoples of the Americas|Native American]] peoples, especially in [[Central America]], [[Peru]], and [[Colombia]].
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In addition, the southeast corner of the [[Black Sea]] was famed for its gold. Exploitation is said to date from the time of [[Midas]], and this gold was important in the establishment of what was probably the world's earliest [[coin]]age in [[Lydia]] between 643 and 630 <small>B.C.E.</small>
  
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Gold in antiquity was relatively easy to obtain geologically; however, 75% of all gold ever produced has been extracted since [[1910]].[http://www.goldsheetlinks.com/production2.htm] It has been estimated that all the gold in the world that has ever been refined would form a single cube [[1 E2 m|20 m]] (66 ft) a side.
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In the history of Western [[alchemy]], its practitioners were fascinated with the idea of producing gold from cheaply available substances. Alchemists, who regarded gold as the king of metals, searched in vain for the [[philosopher's stone]] that was expected to convert [[lead (element)|lead]] or [[mercury (element)|mercury]] into gold. Despite their failure in this pursuit, they discovered various chemical processes and produced new materials, and their work laid a foundation for today's [[chemistry]]. Their symbol for gold was the circle with a point at its center (&#x2609;), which was also the [[astrology|astrological]] symbol, the [[Egypt]]ian [[Egyptian hieroglyph|hieroglyph]], and the ancient Chinese character for the [[Sun]] (now &#26085;).
  
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The primary goal of the [[alchemy|alchemists]] was to produce gold from other substances, such as [[lead]] &mdash; presumably by the interaction with a mythical substance called the [[philosopher's stone]]. 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]]. Their symbol for gold was the [[circle with a point at its centre|circle with a point at its center]] (&#x2609;), which was also the [[astrology|astrological]] symbol, the [[Egypt]]ian [[Egyptian hieroglyph|hieroglyph]] and the ancient [[Chinese character]] for the [[Sun]] (now &#26085;). For modern attempts to produce artificial gold, see [[gold synthesis]].
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Given its historically high value, gold has been the object of thieves and conquerors for thousands of years. For instance, the tombs of the Egyptian pharaohs were plundered for their gold and other valuables. In more recent years, there have been spectacular gold heists at banks and airports.
  
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During the [[19th century]], [[gold rush]]es occurred whenever large gold deposits were discovered, including the [[California gold rush|California]], [[Colorado gold rush|Colorado]], [[Central Otago goldrush|Otago]], [[Australia]], [[Witwatersrand]], [[Black Hills]], and [[Klondike, Yukon|Klondike]] gold rushes.
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The European conquest of South and Central America was fueled in no small part by reports of the gold ornaments displayed in great profusion by [[Native American]] peoples, especially in [[Mexico]], [[Peru]], and [[Colombia]].
  
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Because of its historically high value, much of the gold mined throughout history is still in circulation in one form or another.
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During the nineteenth century, [[gold rush]]es occurred whenever large gold deposits were discovered. They included the California, Colorado, Otago, Australia, Witwatersrand, Black Hills, and Klondike gold rushes.
  
 
==Occurrence==
 
==Occurrence==
 
[[Image:GoldNuggetUSGOV.jpg|thumb|left|200px|A gold nugget]]
 
[[Image:GoldNuggetUSGOV.jpg|thumb|left|200px|A gold nugget]]
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[[Image:Native gold nuggets.jpg|200px|right|thumb|Raw gold from California (top) and Australia (bottom), showing [[octahedron|octahedral]] formations]]
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[[Image:Native gold nuggets.jpg|200px|right|thumb|Raw gold from California (top) and Australia (bottom), showing [[octahedron|octahedral]] formations.]]
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Gold is widely distributed in the Earth's [[Crust (geology)|crust]], at a background level of 0.03 [[gram|g]]/1000 [[kilogram|kg]] (0.03 [[Parts per million|ppm]] by weight). In sea water, its concentration ranges between 0.1 and 2 [[milligram|mg]]/[[tonne|t]] (0.1 to 2 [[Parts per billion|ppb]] by weight), depending on sample location.
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Scientists theorize that the gold on our planet was first formed in an ancient star shortly before it exploded as a supernova. The debris from that explosion is thought to have gone into the formation of our solar system.
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Given its relative chemical inertness, gold usually occurs as the native metal or as an alloy with silver and other precious metals. Occasionally, it has been found in the form of large accumulations, or nuggets. More often, it is found as tiny grains that occur as inclusions within minerals or lie between mineral-grain boundaries. In addition, extremely minute quantities of gold are distributed across the Earth's [[Crust (geology)|crust]] and in seawater.
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There are several types of primary deposits of gold; common ones are termed ''reef'' or ''[[vein]]''. [[Hydrothermal]] [[ore]] deposits of gold occur in [[metamorphic rock]]s and [[igneous rock]]s. In addition, sedimentary black [[shale]] and [[limestone]] deposits contain finely disseminated gold and other metals.
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The primary deposits are weathered and eroded, with most of the gold being transported into stream beds where it congregates with other heavy minerals to form what are called ''alluvial deposits'' or ''placer deposits.'' Recent research shows that microbes may also play a role in transporting and precipitating gold to form grains and nuggets that collect in alluvial deposits.
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[http://www.abc.net.au/science/news/enviro/EnviroRepublish_1032376.htm]
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Gold is commonly associated with [[quartz]] and sulfide minerals. The most common sulfide associations are [[pyrite]], [[chalcopyrite]], [[galena]], [[sphalerite]], [[arsenopyrite]], [[stibnite]], and [[pyrrhotite]]. Iron pyrite (FeS<sub>2</sub>), with its metallic luster and yellowish color, has been called ''fool's gold''; but it may contain small amounts of actual gold.
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==Notable characteristics==
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In chemistry, gold is given the symbol '''Au''', from the [[Latin]] word ''aurum.'' Its [[atomic number]] (the number of protons in the nucleus of each atom) is 79. In the [[periodic table]], it is placed in the same family (group 11 or 1B) as [[copper]] and [[silver]]. Also, it lies in period 6, between [[platinum]] and [[mercury]]. It occurs as one stable [[isotope]] (Au-197) and 18 [[radioisotope]]s.
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Although most other metals are silvery gray in color, gold is distinguished by its deep [[yellow]] hue. When finely divided, it may appear [[black]] or [[ruby]]-colored. [[Colloid]]al solutions (suspensions of tiny gold particles) are intensely colored and often [[purple]].
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Gold is a good conductor of [[heat]] and [[electricity]]. It is a soft metal and the most malleable and ductile of all. A single ounce (troy ounce) of gold can be beaten into a sheet of area 300 square feet or drawn into a wire that extends more than 40 miles.
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Alloys of gold are often prepared to increase its strength or create a range of exotic colors. Adding [[copper]] yields a redder metal; [[iron]], blue; [[silver]], green; [[aluminum]], purple; and [[platinum]], white. When natural [[bismuth]] is added to alloys with silver, the resultant mixture is black. Native gold usually contains 8–10 percent silver, but often much more. An alloy containing 20 percent or more of silver is called [[electrum]]. As the amount of silver increases, the color becomes whiter and the specific gravity lower.
  
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Given its relative chemical inertness, gold usually occurs as the native metal or alloy. Occasionally, it may be found in the form of large accumulations ([[gold nugget|nuggets]]), but it is more often found as minute grains. These grains may lie between mineral grain boundaries or as inclusions within minerals.
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Heat, moisture, [[oxygen]], and most chemical [[reagent]]s have very little chemical effect on gold. This resistance to attack by other agents is the reason why gold came to be classified as a [[noble metal]].
  
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The primary source of gold is usually [[igneous rock]]s or surface concentrations. A deposit usually needs some form of secondary enrichment to form an economically viable ore deposit: either chemical or physical processes like [[erosion]] or dissolution, or more generally [[metamorphism]], which concentrates the gold in sulfide minerals or quartz.
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Gold does, however, react with [[halogen]]s&mdash;such as [[chlorine]], [[bromine]], and [[iodine]]&mdash;to form compounds such as gold (III) chloride (auric chloride, AuCl<sub>3</sub>), gold (III) bromide (auric bromide, AuBr<sub>3</sub>), and gold (I) iodide (aurous iodide, AuI). In such compounds, gold is said to have an ''[[oxidation state]]'' or ''[[oxidation number]]'' of +3 or +1, depending on the number of halogen atoms that have combined with each atom of gold.
  
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There are several primary deposit types; common ones are termed reef or vein. Primary deposits can be weathered and eroded, with most of the gold being transported into stream beds where it congregates with other heavy minerals to form [[placer deposit]]s. In all these deposits, the gold remains in its native form. In addition, [[sedimentary]] black [[shale]] and [[limestone]] deposits contain finely disseminated gold and other [[platinum]] group metals.
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Moreover, gold can be dissolved by [[aqua regia]] (a mixture of nitric acid and hydrochloric acid in the ratio 1:3) to form chlorauric acid (HAuCl<sub>4</sub>). Aqua regia, the Latin term for “royal water,” was so named because it could dissolve the king of metals.
  
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Common gold associations are [[quartz]], often as [[vein]]s, and sulfide minerals. The most common sulfide associations are [[pyrite]], [[chalcopyrite]], [[galena]], [[sphalerite]], [[arsenopyrite]], [[stibnite]] and [[pyrrhotite]]. Rarer mineral associations are [[petzite]], [[calaverite]], [[sylvanite]], [[muthmannite]], [[nagyagite]] and [[krennerite]]. [[Hydrothermal]] [[ore]] deposits of gold occur in [[metamorphic rock]]s and [[igneous rock]]s; [[alluvial deposit]]s and [[placer deposit]]s originate from these sources.
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Gold ions in solution are readily [[Precipitation (chemistry)|precipitated]] out as gold metal by the addition of virtually any other metal to the solution. The added metal dissolves, while the gold is displaced from the solution. The gold ions are said to be ''[[reduction (chemistry)|reduced]]'', while the added metal is said to be ''[[oxidation|oxidized]]''. This is a way to recover gold from solution.
  
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Recent research shows that microbes play an important role in the formation of gold deposits. They transport and precipitate gold to form grains and nuggets that collect in alluvial deposits.
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Under extreme conditions, gold can combine with fluorine to produce gold(V) fluoride (AuF<sub>5</sub>). In this case, gold has the oxidation number +5. Unusually for a metal, gold can also form compounds in which its oxidation number is -1. Such compounds contain the Au<sup>-</sup> [[anion]] and are called ''aurides.'' Examples are [[cesium]] auride (CsAu), [[rubidium]] auride (RbAu), and tetramethylammonium auride, (CH<sub>3</sub>)<sub>4</sub>N<sup>+</sup> Au<sup>-</sup>.
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[http://www.abc.net.au/science/news/enviro/EnviroRepublish_1032376.htm]
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Other compounds formed by gold include:
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* [[gold chalcogenides]] (formed with [[oxygen]], [[sulfur]], [[selenium]], or [[tellurium]]);
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* [[gold cluster compound]]s (in which two or more metal atoms are attached to one another);
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* gold [[hydrazine|hydrazide]](AuN<sub>2</sub>H<sub>3</sub>): an olive-green powder, it is one of several explosive compounds known archaically as ''aurum fulminans.''
  
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==Notable characteristics==
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==Symbolism==
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Gold is a metallic element with a characteristic [[yellow]] color, but can also be [[black]] or [[ruby]] when finely divided, while [[colloid]]al solutions are intensely colored and often [[purple]]. These colors are the result of gold's [[plasmon frequency]] lying in the visible range, which causes red and yellow light to be reflected, and blue light to be absorbed.  Only silver colloids exhibit the same interactions with light, albeit at a shorter frequency, making silver colloids yellow in color.
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Historically, gold has been associated with royalty, sanctity, and durability. The New Testament records that gold was one of the gifts offered by the three magi who visited the newborn Jesus. Later, Christian kings wore golden crowns to symbolize their divinely inspired authority. Also, the rituals of various faiths have involved the use of items made of gold.
  
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It is the most [[malleable]] and [[ductility|ductile]] [[metal]] known; a single [[gram]] can be beaten into a sheet of one [[square metre]], or an [[ounce]] into 300 [[square foot|square feet]]. A soft metal, gold will readily form alloys with many other metals.  This can be done to increase its strength, or create several exotic colors, sold for instance in the western [[United States]] to the tourist trade as "[[Black Hills]]" gold. Adding [[copper]] yields a redder metal, [[iron]] blue, Silver produces green, [[aluminium]] purple, [[platinum]] metals white, and natural [[bismuth]] together with silver alloys produce black. Native gold contains usually eight to ten per cent [[silver]], but often much more &mdash; alloys with a silver content over 20% are called [[electrum]]. As the amount of silver increases, the color becomes whiter and the [[Relative density|specific gravity]] lower.
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Wedding rings are traditionally made of gold, as a metaphor for the commitment of undying love between partners in marriage. Also, gold is associated with notable anniversaries, particularly in a 50-year cycle, such as the golden [[wedding anniversary]] or [[golden jubilee]].
  
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Gold is a good conductor of [[heat]] and [[electricity]], and is not affected by [[air]] and most [[reagent]]s. Heat, moisture, [[oxygen]], and most [[corrosion|corrosive]] agents have very little chemical effect on gold, making it well-suited for use in [[coin]]s and [[jewelry]]; conversely, [[halogen]]s will chemically alter gold, and [[aqua regia]] dissolves it.
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Gold medals and decorations are often used to honor those who have made great contributions to society or have won great competitions. Examples are medals awarded to winners of the [[Nobel Prize]] and champions in the [[Olympic Games]]. Also, many award statuettes are plated in gold, such as those given at the [[Academy Awards]], the [[Emmy Awards]], and the [[British Academy Film Awards]].
  
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Common [[oxidation state]]s of gold include +1 (gold(I) or aurous compounds) and +3 (gold(III) or auric compounds). Gold ions in solution are readily [[reduction (chemistry)|reduced]] and [[Precipitation (chemistry)|precipitated]] out as gold metal by the addition of virtually any other metal as the reducing agent. The added metal is [[oxidation|oxidized]] and dissolves allowing the gold to be displaced from solution and be recovered as a solid precipitate.
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A person who is particularly kind-hearted and generous is said to have a "heart of gold." The eminent [[orator]] [[John Chrysostom]] was said to have a "mouth of gold with a silver tongue."
  
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Recent research undertaken by Frank Reith of the Australian National University shows that microbes play an important role in the formation of gold deposits, transporting and precipitating gold to form grains and nuggets that collect in alluvial deposits.
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On the other hand, hearkening back to the time of [[Moses]], worshipping the [[Golden Calf]] has become a symbol of [[idolatry]] and revolt against God. Native Americans of the Sioux tribe called gold "the yellow metal that makes the white man crazy." In [[Communism|Communist]] [[propaganda]], the gold [[pocket watch]] and its fastening gold chain were classified as accessories of the class enemy, namely, the bourgeoisie and industrial tycoons.
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[http://www.abc.net.au/science/news/enviro/EnviroRepublish_1032376.htm]
 
  
 
==Applications==
 
==Applications==
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Pure gold is too soft for ordinary use and is hardened by [[alloy]]ing with silver, copper, and other metals. Gold and its many alloys are most often used in [[jewelry]], [[Coin|coinage]] and as a standard for [[money|monetary]] exchange in many countries. Because of its high electrical conductivity and resistance to corrosion and other desirable combinations of physical and chemical properties, gold also emerged in the late [[20th century]] as an essential industrial metal.
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Pure gold is too soft for ordinary use and is hardened by [[alloy]]ing with silver, copper, and other metals. Gold and its many alloys are most often used in [[jewelry]] and [[Coin|coinage]], and as a standard for [[money|monetary]] exchange in many countries. Given its high electrical conductivity, resistance to corrosion, and other properties, gold emerged in the late twentieth century as an essential industrial metal.
  
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Gold and its compounds now have a wide range of applications, a number of which are listed below.
 
*Gold can be made into thread and used in [[embroidery]].
 
*Gold can be made into thread and used in [[embroidery]].
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*Gold performs critical functions in [[computer]]s, communications equipment, [[spacecraft]], [[jet aircraft]] engines, and a host of other products.
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*Gold is used in restorative dentistry, especially in tooth restorations such as crowns and bridges.
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*The resistance to oxidation of gold has led to its widespread use as thin layers [[Electroplating|electroplated]] on the surface of electrical connectors to ensure a good connection.
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*Being resistant to oxidation, thin layers of gold are [[Electroplating|electroplated]] on the exposed surfaces of electrical connectors to ensure good connections.
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*Gold is used in restorative dentistry especially in tooth restorations such as [[crown (dentistry)|crowns]] and [[bridges]].
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*Gold performs critical functions in [[computer]]s, communications equipment, [[jet aircraft]] engines, and a host of other products.
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*[[Colloidal gold]] (a gold [[nanoparticle]]) is an intensely [[color]]ed solution that is currently studied in many labs for medical, biological and other applications. It is also the form used as gold paint on [[ceramic]]s prior to firing.
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*Being a good reflector of both infrared and visible light, gold is used for protective coatings on many artificial [[satellite]]s.
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*Gold is used as a coating that enables biological material to be viewed under a scanning electron [[microscope]].
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*The gold isotope Au-198 ([[half-life]] 2.7 days) is used as a treatment for [[cancer]] and other diseases.
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*[[Colloidal gold]] (containing [[nanoparticle]]s of gold in suspension) is being studied in many labs for medical, biological, and other applications. It is also the form used as gold paint on [[ceramic]]s prior to firing.
 
*[[Chlorauric acid]] is used in [[photography]] for toning the silver image.
 
*[[Chlorauric acid]] is used in [[photography]] for toning the silver image.
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*[[Gold(III) chloride]] is used as a [[catalyst]] in [[organic chemistry]]. It is also the usual starting point for making other gold [[Inorganic compound|compounds]].  
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*Gold (III) chloride is used as a [[catalyst]] in [[organic chemistry]]. It is also the usual starting point for making other gold compounds.
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* Gold is used as a coating enabling biological material to be viewed under a [[scanning electron microscope]].
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*A gold compound known as [[disodium aurothiomalate]] is a treatment for rheumatoid [[arthritis]], administered intramuscularly. It can, however, also cause photosensitive [[rash]]es, gastrointestinal disturbance, and [[kidney]] damage.
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* Many competitions and honors, such as the [[Olympics]] and the [[Nobel Prize]], award a gold [[medal]] to the winner (with [[silver]] to the second-place finisher, and [[bronze]] to the third.)
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*Gold flake is added to some gourmet sweets and drinks. Called ''[[varak]]'' (or ''varaq'') in India, it has no reactivity and adds no taste but is taken as a delicacy. Some use it to create super-expensive cocktails.
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*Since it is a good reflector of both infrared and visible light, it is used for the protective coatings on many artificial [[satellite]]s.
 
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*[[Disodium aurothiomalate]] is a treatment for rheumatoid [[arthritis]] (administered intramuscularly). It inhibits [[lymphocyte]] proliferation, [[lysosome|lysosomal]] enzyme release, the release of [[reactive oxygen species]] from [[macrophage]]s, and [[IL-1]] production. However, it can also cause photosensitive [[rash]]es, gastrointestinal disturbance, and [[kidney]] damage.
 
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*The gold isotope Au-198, ([[half-life]]: 2.7 days) is used in some [[cancer]] treatments and for treating other diseases.
 
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*Gold flake is used on and in some gourmet sweets and drinks. Called [[varak]] or (varaq) in India.  Having no reactivity it adds no taste but is taken as a delicacy. Some use it as an excuse to create super-expensive delicacies ($1,000 cocktails).  For similar reasons, it also used as the basis for some superstitious, over the top, health claims.  Only the salts and radioisotopes (mentioned above) have any evidence of medicinal value.
 
 
*[[White gold]] (an alloy of gold with [[platinum]], [[palladium]], [[nickel]], and/or [[zinc]]) serves as a substitute for platinum.
 
*[[White gold]] (an alloy of gold with [[platinum]], [[palladium]], [[nickel]], and/or [[zinc]]) serves as a substitute for platinum.
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*[[Green gold]] (a gold/[[silver]] alloy) is used in specialized jewelry while gold alloys with copper (reddish color) are more widely used for that purpose ([[rose gold]]).
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*[[Green gold]] and [[rose gold]] are alloys of gold with [[silver]] and [[copper]], respectively, and are used in specialized jewelry.
  
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==Value==
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It should be noted that the human body does not absorb gold very well. As a result, compounds of gold are normally not very toxic. In dentistry, gold is regarded as the safest and most successful form of restorative material. On the other hand, [[liver]] and [[kidney]] damage has been reported for up to 50 percent of [[arthritis]] patients treated with gold-containing drugs.
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{{See also|Gold as an investment}}
 
  
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[[Image:3sovriegns.jpg|thumb|right|200px|Three [[gold sovereign|Gold Sovereign]]s with a [[Krugerrand]]]]
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==Production==
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[[Image:Goldkey_logo_removed.jpg|thumb|right|200px|Gold bars with [[Krugerrand]]s in the background.]]
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[[Image:Gold mine.jpg|thumb|250px|right|The entrance to an underground gold mine in Victoria, Australia]]
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[[Image:GoldOreUSGOV.jpg|175px|right|thumb|Gold ore]]
  
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Like other precious metals, gold is measured by [[troy weight]] and by [[gram]]s. When it is alloyed with other metals the term ''[[carat (purity)|carat]]'' or ''karat'' is used to indicate the amount of gold present, with 24 carats being pure gold and lower ratings proportionally less. The purity of a gold bar can also be expressed as a decimal figure ranging from 0 to 1, known as the [[millesimal fineness]], such as 0.995.
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According to some estimates, all the gold in the world that has ever been refined would form a single cube 20 meters (66 ft) on each side. About 75 percent of that has been extracted since 1910.
  
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The price of gold is determined on the open market, but a procedure known as the [[Gold Fixing]] in [[London]], originating in 1919, provides a twice-daily benchmark figure to the industry.
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In large, easily mined deposits, economic [[gold extraction]] can be achieved from ore grades as low as 0.5 g/1000 kg (0.5 ppm), on average. Typical ore grades in [[open-pit_mining|open-pit]] mines are 1–5 g/1000 kg (1-5 ppm); ore grades in underground or [[hard_rock_mining|hard rock]] mines are usually at least 3 g/1000 kg (3 ppm), on average. Ore grades of 30 g/1000 kg (30 ppm) are usually needed before gold is visible to the naked eye. Thus, in most gold mines you will not see any gold.
  
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Historically gold was used to back currency in an economic system known as the [[gold standard]] in which one unit of currency was equivalent to a certain [[weight]] of gold. As part of this system, governments and [[central bank]]s attempted to control the price of gold by setting values at which they would exchange it for currency. For a long period the United States government set the price of gold at $20.67 per [[troy weight|troy ounce]] ($664.56/kg) but in [[1934]] the price of gold was set at $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 began to act together to defend the price against market forces.
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===Extraction methods===
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In the past, prospectors found grains and lumps of gold along stream beds. They used the process of ''panning'' to separate the heavier gold pieces from the sand and gravel. Later, various techniques were developed to extract gold from the rocky vein or ''mother lode.'' Some of these are described below.
  
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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 banks still hold historical [[official gold reserves|gold reserves]] as a [[reserves|reserve]] asset although the level has generally been declining. The largest gold depository in the world is that of the [[U.S. Federal Reserve Bank]], in [[New York]].
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*Gravity separation: The rock may be crushed into fine particles, mixed with water, and made to flow down a sloping trough. Gold, being heavier than other particles, gets lodged in riffles in the trough.
  
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Since 1968 the price of gold on the open market has ranged widely, with a record high of $850/oz ($27,300/kg) on [[21 January]] [[1980]], to a low of $252.90/oz ($8,131/kg) on [[21 June]] [[1999]] (London Fixing). Prices have risen to the $500/oz mark in late 2005, due to a depreciation of the US dollar and inflation due to rising energy costs.
+
*Amalgamation: Crushed rock is treated with [[mercury]], which readily dissolves the gold to form a liquid alloy called an ''amalgam.'' The amalgam is separated from the rock and squeezing and heating remove the mercury. The gold is left behind.
  
−
==Gold and the money supply==
+
*Cyanide treatment: Certain [[cyanide]] compounds can be used to dissolve the gold and separate it from the rock. The gold can then be recovered by adding other chemicals to the solution.
−
In January 1959 US M3 money supply was $288.8 billion, and the Official Gold Holdings of the United States was then 17,335.1 Tonnes, or about 557 million ounces (there are 32,150.7 Troy Ounces in a Tonne). That means that in 1959, there were $518 in circulation for every ounce of gold reserves held by the USA. Although the theoretical price should then have been $518 per ounce, the actual price, as fixed under the gold standard was only $35 an ounce.
 
  
−
By August 2005, the US M3 money supply had risen to $9,873.9 billion, whilst at the same time the Official Gold Holdings of the United States had fallen to just 8,133.5 Tonnes, or about 261 million Troy Ounces. This means that today, in 2005, there are $37,831 in circulation for every ounce of gold held by the United States.
+
The downside of gold extraction methods is that if they are not performed with extreme care, they can have harmful effects on the environment. On the one hand, open-pit mining operations tear up the landscape, which needs to be repaired later. On the other hand, chemical extraction techniques can leave residues of toxic chemicals in the environment. Mercury and cyanides are toxic substances, but mercury tends to linger and accumulate, while cyanides break down.
  
−
The above numbers show the falling influence of gold in the monetary system of the world today. [[Goldbug]]s believe, or even hope, that one day gold's importance will return as the printing of paper money gets out of control and we end in a hyper-inflationary fiat money collapse.
+
Gold extracted by the above methods is often alloyed with silver and other metals, and it needs to be refined. Mints in the [[United States]] use a process called ''electrolysis'', which produces nearly pure gold.
  
−
==Restrictions on gold ownership==
+
Chemists have demonstrated the futility of the alchemist's dream of producing gold from other substances via chemical reactions. Interestingly, however, modern science has shown that it is feasible to generate minuscule amounts of gold by artificial [[nucleosynthesis|nuclear transformation]]s in [[particle accelerator]]s. The product is likely to be one or more [[radioactive]] [[isotope]]s of gold.
−
Because of its use as a reserve store of value, the possession of gold is sometimes restricted or banned. Within the United States, the private possession of gold except as jewelry and coin collecting was banned between 1933 and 1975. President [[Franklin D. Roosevelt]] expropriated gold by [http://www.the-privateer.com/1933-gold-confiscation.html Executive Order 6102], and President [[Richard Nixon]] closed the gold window by which foreign countries could exchange American dollars for gold at a fixed rate.
 
  
−
==Return of a gold standard?==
+
The world's oceans hold a vast amount of gold, but at very low concentrations (perhaps 1-2 parts per billion). No commercially viable mechanism for extracting gold from seawater has yet been identified.
−
In the first few years of the [[21st century]], reports started to circulate that [[Malaysia]] was planning a return to the [[gold standard]] — to issue and use [[gold dinar]]s as currency in international trade. The purported purpose of this move would be to reduce dependence on the [[United States dollar]] as a reserve currency, and to establish a non-debt-backed currency in accord with [[Islamic law]] against the charging of interest. [http://www.islamidag.dk/ulamaongold.html] Nonetheless, gold dinar currency has not yet emerged. [http://english.aljazeera.net/NR/exeres/E7515CEE-880E-492F-B225-A94E21D90D2B.htm] [http://www.mineweb.net/columns/american_notes/336075.htm]
 
  
−
==Gold in investment portfolios==
+
===Gold-producing regions around the world===
−
{{main|Gold as an investment}}
+
Since the 1880s, [[South Africa]] has accounted for a large proportion of the world's gold production. In 1970 South Africa's production of gold, about 1,000 tons, was 79 percent of the global total. By 2004, however, the country's production had fallen to 342 tons as a result of the increasing difficulty of extraction and changing economic factors affecting the industry in South Africa.
−
As a [[tangible investment]] gold is sometimes held as part of a portfolio because over the long term gold has an extensive history of maintaining its value. It has in the last century gained ground in relation to fiat currencies owing to [[inflation]].  Gold becomes particularly desirable in times of extremely weak confidence and during [[hyperinflation]] because gold maintains its value even as [[fiat money]] becomes worthless. People who enjoy investing in gold are known as [[goldbug]]s.
 
  
−
[[Futures contract]]s based on gold currently trade on various exchanges around the world. In the US this occurs primarily on [[COMEX]] (Commodity Exchange) which is a subsidiary of the [[New York Mercantile Exchange]]. Speculation about the future price of gold and other commodities is carried on at COMEX. Recently, gold-based [[Exchange-traded_fund|ETFs]] like [http://finance.yahoo.com/q?s=GLD GLD] have emerged as a more convenient investment vehicle.
+
The city of [[Johannesburg]] was built atop the world's greatest gold finds. Gold fields in the [[Orange Free State]] and the [[Transvaal]] are deep and require the world's deepest mines. The [[Second Boer War]] of 1899&ndash;1901, between the [[British Empire]] and the white [[Boers]], was at least partly over the rights of miners and possession of the gold wealth in South Africa. The Indian city of [[Kolar Gold Fields|Kolar]] is also built on a great gold deposit.  
  
−
In some countries such as Switzerland, it is possible to hold physical gold as part of an investment portfolio, due to the absence of taxes and narrow bid-ask spreads, however in other countries portfolio managers sometimes hold gold shares or gold bullion securities as a proxy for the metal itself.  [[Exchange Traded Fund]]s such as Gold Bullion Securities are securities sponsored by the World Gold Council and which are fully backed up by allocated gold held by a custodian. The main Gold Bullion Securities are as follows:
+
Other major producers are [[Canada]], the [[United States]], and [[Australia]]. Mines in [[U.S. State|South Dakota]] and Nevada supply two-thirds of the gold used in the United States. The [[Siberia]]n regions of [[Russia]] used to be significant in the global gold mining industry. In South America, the controversial project [[Pascua Lama]] aims at exploitation of rich fields in the high mountains of [[Atacama]], at the border between [[Chile]] and [[Argentina]].
  
−
*New York Stock Exchange (NYSE), Symbol:GLD (Streettracks Gold Shares, ISIN No. US8633071043)
+
==Monetary value==
−
*London Stock Exchange (LSE) Symbol GBS (Gold Bullion Securities ISIN No. GB00B00FHZ82)
+
{{See also|Gold as an investment}}
−
*Euronext France Symbol:GBS (Gold Bullion Securities ISIN No. GB00B00FHZ82 )
 
−
*Australian Stock Exchange (ASX), Symbol:GOLD (Gold Bullion Securities ISIN No. AU00000GOLD7)
 
−
*Johannesburg Securities Exchange (JSE), Symbol:GLD (New Gold Debentures ISIN No. ZAE000060067 )
 
  
−
==Production==
+
Like other precious metals, gold is measured by [[troy weight]] or [[gram]]s. When alloyed with other metals, the term ''[[carat (purity)|carat]]'' ''(karat)'' is used to indicate the proportion of gold present. Pure gold is given the value 24 carats, and lower ratings correspond to proportionally less gold. The purity of a gold bar may also be expressed as a decimal figure ranging from 0 to 1, known as the [[millesimal fineness]].
−
[[Image:Gold mine.jpg|thumb|250px|right|The entrance to an underground gold mine in Victoria, Australia]]
 
−
[[Image:GoldOreUSGOV.jpg|175px|right|thumb|Gold ore]]
 
−
Economic [[gold extraction]] can be achieved from ore grades as little as 0.5 g/1000 kg (0.5 ppm) on average in large easily mined deposits, typical ore grades in [[open-pit_mining|open-pit]] mines are 1–5 g/1000 kg (1-5 ppm), ore grades in underground or [[hard_rock_mining|hard rock]] mines are usually at least 3 g/1000 kg (3 ppm) on average. Ore grades of 30 g/1000 kg (30 ppm) are usually needed before gold is visible to the naked eye, therefore in most gold mines you will not see any gold. It is claimed, that all the gold that has been mined throughout the history of mankind could be incorporated in a solid ball with a diameter of 27 [[metre]]s.
 
  
−
Since the 1880s [[South Africa]] has been the source for a large proportion of the world's gold supply. Production in 1970 accounted for 79% of the world supply, producing about 1,000 tonnes, however production in 2004 was 342 tonnes. This decline was due to the increasing difficulty of extraction and changing economic factors affecting the industry in South Africa.
+
===Price of gold===
 +
[[Image:Goldkey_logo_removed.jpg|thumb|right|200px|Gold bars with [[Krugerrand]]s in the background.]]
  
−
The city of [[Johannesburg]] was built atop the world's greatest gold finds. Gold fields in the [[Orange Free State]] and the [[Transvaal]] are deep and require the world's deepest mines. The [[Second Boer War]] of [[1899]]&ndash;[[1901]] between the [[British Empire]] and the white [[Boers]] was at least partly over the rights of miners and possession of the gold wealth in South Africa.
+
The price of gold is determined on the open market, but a procedure known as the [[Gold Fixing]] in [[London]], originating in 1919, provides a twice-daily benchmark figure to the industry.
  
−
Other major producers are [[Canada]], [[United States]] and [[Western Australia]]. Mines in [[South Dakota]] and [[Nevada]] supply two-thirds of gold used in the United States. [[Siberian]] regions of the [[USSR]] also used to be significant in the global gold mining industry. [[Kolar Gold Fields]] in [[India]] is another example of a city being built on the greatest gold deposits in [[India]]. In South America, the controversial project [[Pascua Lama]] aims at exploitation of rich fields in the high mountains of [[Atacama]], at the border between [[Chile]] and [[Argentina]].
+
Historically, gold was used to back currency in an economic system called the [[gold standard]], in which one unit of currency was equivalent to a certain [[weight]] of gold. In this system, governments and [[central bank]]s attempted to control the price of gold by setting values at which they would exchange it for currency. For a long period, the U.S. government set the price of gold at $20.67 per troy ounce ($664.56/kg), but in 1934, the price of gold was set at $35.00 per troy ounce ($1125.27/kg). By 1961, it was becoming hard to maintain this price, and a pool of U.S. and European banks began acting together to defend the price against market forces.
  
−
The idea of producing gold out of lesser metals or other cheap substances has fascinated people throughout the centuries. Scientists, kings and [[charlatan]]s obsessed with the secret art of [[alchemy]] accidentally invented practically useful materials (e.g. [[porcelain]]), while searching in vain for the [[philosopher's stone]], which was supposed to turn [[mercury (element)|mercury]] into gold. Modern science has since proven the impossibility of making gold from other elements via chemical reactions.
+
On March 17, 1968, economic circumstances led to 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 value of $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 banks still hold historical [[official gold reserves|gold reserves]] as assets, although these levels have generally been declining. The largest gold depository in the world is that of the [[U.S. Federal Reserve Bank]] in [[New York]].
  
−
However, it is possible to obtain infinitesimally small amounts of gold by artificial [[nucleosynthesis|nuclear transformation]]s in [[particle accelerator]]s The gold [[isotope]]s produced would likely be [[radioactive]]. No [[economically feasible]] method to manufacture gold artificially has been found and published yet. The possibility of cheap man-made gold would have unforeseen economic and [[political]] consequences.
+
Since 1968, the price of gold on the open market has ranged widely, with a record 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 Fixing). In late 2005, prices rose to the $500/oz mark, due to a depreciation of the U.S. dollar and inflation driven by rising energy costs.
  
−
The world's oceans hold a vast amount of gold, but in very low concentrations (perhaps 1-2 parts per billion). [[Fritz Haber]]
+
===Gold and the money supply===
−
(the German inventor of the [[Haber process]]) attempted
+
In January 1959, the U.S. M3 money supply (the broadest measure of money used by economists) was $288.8 billion, and the Official Gold Holdings of the United States was 17,335.1 tons, or 557 million ounces (there are 32,150.7 troy ounces in a ton). In other words, in 1959, there were $518 in circulation for every ounce of gold reserves held by the United States. The theoretical price should then have been $518 per ounce, but the actual price (fixed under the gold standard) was only $35 per ounce.
−
commercial extraction of gold from sea water in an effort to help pay Germany's reparations following the [[First World War]]. Unfortunately, his assessment of the concentration
 
−
of gold in sea water was unduly high, probably due to sample contamination. The effort produced little gold and cost the German government far more than the commercial value of the gold recovered. No commercially viable mechanism for performing gold extraction from sea water has yet been identified.
 
  
−
==Compounds/isotopes==
+
By August 2005, the U.S. M3 money supply had risen to $9,873.9 billion, while the Official Gold Holdings had fallen to just 8,133.5 tons, or about 261 million troy ounces. This means that in 2005, there were $37,831 in circulation for every ounce of gold held by the United States. These numbers show the falling influence of gold in the monetary system of the world.  
−
Although gold is a [[noble metal]], it can form many compounds, auric chloride  (Au[[chlorine|Cl]]<sub>3</sub>) and chlorauric acid ([[hydrogen|H]]AuCl<sub>4</sub>) being the most common. Gold compounds can be aurous (univalent, +1) or auric (trivalent, +3). Under extreme conditions, it combines with fluorine to take a +5 state (gold pentafluoride, AuF<sub>5</sub>). Unusually for a metal, it occasionally forms compounds in which it is an [[anion]], Au<sup>-1</sup>. Examples are [[caesium]] auride (CsAu) and [[rubidium]] auride (RbAu), and tetramethylammonium auride, (CH<sub>3</sub>)<sub>4</sub>N<sup>+</sup> Au<sup>-</sup>.
 
  
−
Gold also forms:
+
===Gold in investment portfolios===
−
*The AuCl<sub>4</sub><sup>-</sup> ion after dissolving in [[aqua regia]]
 
−
*[[Gold halide]]s ([[fluorine|F]],[[chlorine|Cl]],[[bromine|Br]],[[iodine|I]])
 
−
*[[Gold chalcogenides]] ([[oxygen|O]], [[sulfur|S]], [[selenium|Se]],[[tellurium|Te]])
 
−
*[[Gold cluster compound]]s
 
−
*Gold [[hydrazine|hydrazide]]: an olive-green powder, AuN<sub>2</sub>H<sub>3</sub>, one of several explosive compounds known archaically as ''aurum fulminans''
 
  
−
There is only one stable [[isotope]] of gold, and 18 [[radioisotope]]s with Au-195 being the most stable with a [[half-life]] of 186 days.
+
As a [[tangible investment]], gold is sometimes held as part of a portfolio because it has an extensive history of maintaining its value over the long term. In the last century, it has gained ground in relation to fiat currencies owing to [[inflation]]. Gold becomes particularly desirable in times of extremely weak confidence and during [[hyperinflation]] because it maintains its value even as [[fiat money]] becomes worthless. People who enjoy investing in gold are known as [[gold bug]]s. Many of them believe, or even hope, that one day gold's importance will return as the printing of paper money gets out of control and we end in a hyper-inflationary fiat money collapse.
  
−
==Precautions==
+
In some countries such as Switzerland, it is possible to hold physical gold as part of an investment portfolio. In other countries, however, portfolio managers may hold gold shares or gold bullion securities as proxies for the metal itself. [[Exchange-traded fund]]s (ETFs), such as gold bullion securities, are sponsored by the World Gold Council and are fully backed by allocated gold held by a custodian.
−
The human body doesn't absorb gold very well, thus compounds of gold are not normally very toxic. [[Liver]] and [[kidney]] damage has, however, been reported for up to 50% of arthritis patients treated with gold-containing drugs. Gold used in dentistry is widely regarded as the safest form of restorative material, as well as the most successful.
 
  
−
==Symbolism==
+
===Restrictions on gold ownership===
−
Historically, gold has been associated with royalty, sanctity, and durability. The New Testament records that gold was one of the gifts offered by the three magi who visited the newborn Jesus. Later, Christian kings wore golden crowns to symbolize their divinely inspired authority. Also, various religious rituals have involved the use of items made of gold. The tombs of the pharaohs of ancient Egypt were filled with items made of or plated with gold.
+
Because of its use as a reserve store of value, the possession of gold is sometimes restricted or banned. Within the United States, the private possession of gold except as jewelry and coin collecting was banned between 1933 and 1975. President [[Franklin D. Roosevelt]] expropriated gold by [http://www.the-privateer.com/1933-gold-confiscation.html Executive Order 6102], and President [[Richard Nixon]] closed the gold window by which foreign countries could exchange American dollars for gold at a fixed rate.
  
−
Wedding rings are traditionally made of gold, as a metaphor for the unchanging commitment of the partners in marriage. Also, gold is associated with notable anniversaries, particularly in a 50-year cycle, such as the golden [[wedding anniversary]] or [[golden jubilee]].
+
==Controversies==
 +
In the twenty first century, gold is at the center of a swirling controversy over its uses and value in relation to the environmental costs of producing it. The two sides of the issue are finely drawn and both present persuasive arguments supporting their view. On the one side are environmentally conscious people, mostly from the developed countries, who point both to the high environmental costs of gold mining, including huge volumes of water consumed and landscapes chewed up and contaminated with cyanide or mercury and the fact that the largest single use of gold is for gold jewelry. On the other side are representatives of the gold mining industry who point to the very significant economic benefits to the countries hosting the gold mining operations and point out that in many developing countries with high inflation rates gold is perhaps the most reliable form of wealth. They further point out that in much of India gold jewelry is the only form of wealth that many woman traditionally could own, so the jewelry is much more than a vanity possession, it is an essential element for a woman's financial security.
  
−
Gold medals and decorations are often used to honor those who have made great contributions to society or have won great competitions. Examples are medals awarded to winners of the [[Nobel Prize]] and champions in the [[Olympic Games]]. Also, many award statuettes are plated in gold, such as those given at the [[Academy Awards]], the [[Emmy Awards]], and the [[British Academy Film Awards]].
+
With its many special properties and deep ties to financial markets, greed, high technology, environmental desecration, beauty, vanity, and, for some of the lesser developed countries, development, education, and economic security, gold in many ways embodies the best and the worst of humanity. In the coming decades the fate of gold may well be seen as a monitor of the progress of humanity toward a peaceful, happy world.
−
 
 
−
A person who is particularly kind-hearted and generous is said to have a "heart of gold." The eminent [[orator]] [[John Chrysostom]] was said to have a "mouth of gold with a silver tongue."
 
−
 
 
−
On the other hand, hearkening back to the time of Moses, worshipping the [[Golden Calf]] has become a symbol of [[idolatry]] and revolt against God. Native Americans of the Sioux tribe called gold "the yellow metal that makes the white man crazy." In [[Communist]] [[propaganda]], the gold [[pocket watch]] and its fastening gold chain were classified as accessories of the class enemy, namely, the bourgeoisie and industrial tycoons.
 
  
 
==References==
 
==References==
−
*[http://periodic.lanl.gov/elements/79.html Los Alamos National Laboratory &ndash; Gold]
+
*[http://www.infoplease.com/ce6/sci/A0821152.html The Columbia Electronic Encyclopedia, 6th ed] Retrieved June 24, 2017.
−
*[http://www.infoplease.com/ce6/sci/A0821152.html The Columbia Electronic Encyclopedia, 6th ed]
+
*[http://www.webelements.com/webelements/elements/text/Au/index.html WebElements.com &ndash; Gold] Retrieved June 24, 2017.
 +
*[http://www.bbc.co.uk/dna/h2g2/A3327103 BBC - h2g2 - Gold] Retrieved June 24, 2017.
  
−
==See also==
+
==External links==
−
* [[Gold prospecting]]
+
All links retrieved June 24, 2017.
−
* [[Gold as an investment]]
 
−
* [[Colloidal gold]]
 
−
* [[Socialism and Gold]]
 
−
* [[22/22k]]
 
  
−
==External links==
 
−
{{Commons|Gold}}
 
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*[http://www.webelements.com/webelements/elements/text/Au/index.html WebElements.com &ndash; Gold] (also used as a reference)
 
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*[http://mineral.galleries.com/minerals/elements/gold/gold.htm Mineral Galleries - Native Gold]
 
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*[http://www.lateralscience.co.uk/gold/auriferous.html ''Getting Gold'' 1898 book]
 
−
*[http://www.bbc.co.uk/dna/h2g2/A3327103 BBC - h2g2 - Gold]
 
 
*[http://www.silver-colloids.com/Pubs/history-gold.html Silver Colloids &ndash; A Brief History of the Health Support Uses of Gold]
 
*[http://www.silver-colloids.com/Pubs/history-gold.html Silver Colloids &ndash; A Brief History of the Health Support Uses of Gold]
  
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Latest revision as of 08:13, 24 January 2023


79 platinum ← gold → mercury
Ag
↑
Au
↓
Rg
Au-TableImage.png
periodic table
General
Name, Symbol, Number gold, Au, 79
Chemical series transition metals
Group, Period, Block 11, 6, d
Appearance metallic yellow
Native gold nuggets.jpg
Atomic mass 196.966569(4) g/mol
Electron configuration [Xe] 4f14 5d10 6s1
Electrons per shell 2, 8, 18, 32, 18, 1
Physical properties
Phase solid
Density (near r.t.) 19.3 g/cm³
Liquid density at m.p. 17.31 g/cm³
Melting point 1337.33 K
(1064.18 °C, 1947.52 °F)
Boiling point 3129 K
(2856 °C, 5173 °F)
Heat of fusion 12.55 kJ/mol
Heat of vaporization 324 kJ/mol
Heat capacity (25 °C) 25.418 J/(mol·K)
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 1646 1814 2021 2281 2620 3078
Atomic properties
Crystal structure cubic face centered
Oxidation states 3, 1
(amphoteric oxide)
Electronegativity 2.54 (Pauling scale)
Ionization energies 1st: 890.1 kJ/mol
2nd: 1980 kJ/mol
Atomic radius 135 pm
Atomic radius (calc.) 174 pm
Covalent radius 144 pm
Van der Waals radius 166 pm
Miscellaneous
Magnetic ordering no data
Electrical resistivity (20 °C) 22.14 nΩ·m
Thermal conductivity (300 K) 318 W/(m·K)
Thermal expansion (25 °C) 14.2 µm/(m·K)
Speed of sound (thin rod) (r.t.) (hard-drawn)
2030 m/s
Speed of sound (thin rod) (r.t.) 78 m/s
Shear modulus 27 GPa
Bulk modulus 220 GPa
Poisson ratio 0.44
Mohs hardness 2.5
Vickers hardness 216 MPa
Brinell hardness 2450 MPa
CAS registry number 7440-57-5
Notable isotopes
Main article: Isotopes of gold
iso NA half-life DM DE (MeV) DP
195Au syn 186.10 d ε 0.227 195Pt
196Au syn 6.183 d ε 1.506 196Pt
β- 0.686 196Hg
197Au 100% Au is stable with 118 neutrons
198Au syn 2.69517 d β- 1.372 198Hg
199Au syn 3.169 d β- 0.453 199Hg

Gold (chemical symbol Au; atomic number 79) has long been valued as a noble metal and a symbol of purity, durability, and royalty. Its attractive yellow shine, resistance to corrosion, and relative rarity have made it extremely appealing for use in jewelry, ornaments, and coinage. Kings have chosen to wear golden crowns, and couples have expressed their undying love with gold wedding rings. Yet the attractiveness of gold has also brought out the worst of human nature, as it has been an object of thieves and conquerors. In recent years, gold has been incorporated in a wide variety of products, including computers, communications hardware, aircraft, and spacecraft, and newer applications continue to be tested.

History

Crown of the Austrian Empire

Gold (Sanskrit jval, Greek χρυσος [khrusos], Latin aurum for "shining dawn," Anglo-Saxon gold, Chinese 金 [jīn], Japanese 金 [kin]) is a chemical element and a precious metal that has been known and highly valued since prehistoric times. Early peoples used it mainly for ornamentation and rituals.

Gold is described in Egyptian hieroglyphs dating back to 2600 B.C.E., and it is mentioned several times in the Hebrew scriptures. Ancient Egypt and Nubia had the resources to make them major gold-producing areas. The tombs of the Egyptian pharaohs were filled with items made of, or plated with, gold.

In addition, the southeast corner of the Black Sea was famed for its gold. Exploitation is said to date from the time of Midas, and this gold was important in the establishment of what was probably the world's earliest coinage in Lydia between 643 and 630 B.C.E.

In the history of Western alchemy, its practitioners were fascinated with the idea of producing gold from cheaply available substances. Alchemists, who regarded gold as the king of metals, searched in vain for the philosopher's stone that was expected to convert lead or mercury into gold. Despite their failure in this pursuit, they discovered various chemical processes and produced new materials, and their work laid a foundation for today's chemistry. Their symbol for gold was the circle with a point at its center (☉), which was also the astrological symbol, the Egyptian hieroglyph, and the ancient Chinese character for the Sun (now 日).

Given its historically high value, gold has been the object of thieves and conquerors for thousands of years. For instance, the tombs of the Egyptian pharaohs were plundered for their gold and other valuables. In more recent years, there have been spectacular gold heists at banks and airports.

The European conquest of South and Central America was fueled in no small part by reports of the gold ornaments displayed in great profusion by Native American peoples, especially in Mexico, Peru, and Colombia.

During the nineteenth century, gold rushes occurred whenever large gold deposits were discovered. They included the California, Colorado, Otago, Australia, Witwatersrand, Black Hills, and Klondike gold rushes.

Occurrence

A gold nugget
Raw gold from California (top) and Australia (bottom), showing octahedral formations.

Scientists theorize that the gold on our planet was first formed in an ancient star shortly before it exploded as a supernova. The debris from that explosion is thought to have gone into the formation of our solar system.

Given its relative chemical inertness, gold usually occurs as the native metal or as an alloy with silver and other precious metals. Occasionally, it has been found in the form of large accumulations, or nuggets. More often, it is found as tiny grains that occur as inclusions within minerals or lie between mineral-grain boundaries. In addition, extremely minute quantities of gold are distributed across the Earth's crust and in seawater.

There are several types of primary deposits of gold; common ones are termed reef or vein. Hydrothermal ore deposits of gold occur in metamorphic rocks and igneous rocks. In addition, sedimentary black shale and limestone deposits contain finely disseminated gold and other metals.

The primary deposits are weathered and eroded, with most of the gold being transported into stream beds where it congregates with other heavy minerals to form what are called alluvial deposits or placer deposits. Recent research shows that microbes may also play a role in transporting and precipitating gold to form grains and nuggets that collect in alluvial deposits. [1]

Gold is commonly associated with quartz and sulfide minerals. The most common sulfide associations are pyrite, chalcopyrite, galena, sphalerite, arsenopyrite, stibnite, and pyrrhotite. Iron pyrite (FeS2), with its metallic luster and yellowish color, has been called fool's gold; but it may contain small amounts of actual gold.

Notable characteristics

In chemistry, gold is given the symbol Au, from the Latin word aurum. Its atomic number (the number of protons in the nucleus of each atom) is 79. In the periodic table, it is placed in the same family (group 11 or 1B) as copper and silver. Also, it lies in period 6, between platinum and mercury. It occurs as one stable isotope (Au-197) and 18 radioisotopes.

Although most other metals are silvery gray in color, gold is distinguished by its deep yellow hue. When finely divided, it may appear black or ruby-colored. Colloidal solutions (suspensions of tiny gold particles) are intensely colored and often purple.

Gold is a good conductor of heat and electricity. It is a soft metal and the most malleable and ductile of all. A single ounce (troy ounce) of gold can be beaten into a sheet of area 300 square feet or drawn into a wire that extends more than 40 miles.

Alloys of gold are often prepared to increase its strength or create a range of exotic colors. Adding copper yields a redder metal; iron, blue; silver, green; aluminum, purple; and platinum, white. When natural bismuth is added to alloys with silver, the resultant mixture is black. Native gold usually contains 8–10 percent silver, but often much more. An alloy containing 20 percent or more of silver is called electrum. As the amount of silver increases, the color becomes whiter and the specific gravity lower.

Heat, moisture, oxygen, and most chemical reagents have very little chemical effect on gold. This resistance to attack by other agents is the reason why gold came to be classified as a noble metal.

Gold does, however, react with halogens—such as chlorine, bromine, and iodine—to form compounds such as gold (III) chloride (auric chloride, AuCl3), gold (III) bromide (auric bromide, AuBr3), and gold (I) iodide (aurous iodide, AuI). In such compounds, gold is said to have an oxidation state or oxidation number of +3 or +1, depending on the number of halogen atoms that have combined with each atom of gold.

Moreover, gold can be dissolved by aqua regia (a mixture of nitric acid and hydrochloric acid in the ratio 1:3) to form chlorauric acid (HAuCl4). Aqua regia, the Latin term for “royal water,” was so named because it could dissolve the king of metals.

Gold ions in solution are readily precipitated out as gold metal by the addition of virtually any other metal to the solution. The added metal dissolves, while the gold is displaced from the solution. The gold ions are said to be reduced, while the added metal is said to be oxidized. This is a way to recover gold from solution.

Under extreme conditions, gold can combine with fluorine to produce gold(V) fluoride (AuF5). In this case, gold has the oxidation number +5. Unusually for a metal, gold can also form compounds in which its oxidation number is -1. Such compounds contain the Au- anion and are called aurides. Examples are cesium auride (CsAu), rubidium auride (RbAu), and tetramethylammonium auride, (CH3)4N+ Au-.

Other compounds formed by gold include:

  • gold chalcogenides (formed with oxygen, sulfur, selenium, or tellurium);
  • gold cluster compounds (in which two or more metal atoms are attached to one another);
  • gold hydrazide(AuN2H3): an olive-green powder, it is one of several explosive compounds known archaically as aurum fulminans.

Symbolism

Historically, gold has been associated with royalty, sanctity, and durability. The New Testament records that gold was one of the gifts offered by the three magi who visited the newborn Jesus. Later, Christian kings wore golden crowns to symbolize their divinely inspired authority. Also, the rituals of various faiths have involved the use of items made of gold.

Wedding rings are traditionally made of gold, as a metaphor for the commitment of undying love between partners in marriage. Also, gold is associated with notable anniversaries, particularly in a 50-year cycle, such as the golden wedding anniversary or golden jubilee.

Gold medals and decorations are often used to honor those who have made great contributions to society or have won great competitions. Examples are medals awarded to winners of the Nobel Prize and champions in the Olympic Games. Also, many award statuettes are plated in gold, such as those given at the Academy Awards, the Emmy Awards, and the British Academy Film Awards.

A person who is particularly kind-hearted and generous is said to have a "heart of gold." The eminent orator John Chrysostom was said to have a "mouth of gold with a silver tongue."

On the other hand, hearkening back to the time of Moses, worshipping the Golden Calf has become a symbol of idolatry and revolt against God. Native Americans of the Sioux tribe called gold "the yellow metal that makes the white man crazy." In Communist propaganda, the gold pocket watch and its fastening gold chain were classified as accessories of the class enemy, namely, the bourgeoisie and industrial tycoons.

Applications

Pure gold is too soft for ordinary use and is hardened by alloying with silver, copper, and other metals. Gold and its many alloys are most often used in jewelry and coinage, and as a standard for monetary exchange in many countries. Given its high electrical conductivity, resistance to corrosion, and other properties, gold emerged in the late twentieth century as an essential industrial metal.

Gold and its compounds now have a wide range of applications, a number of which are listed below.

  • Gold can be made into thread and used in embroidery.
  • Gold is used in restorative dentistry, especially in tooth restorations such as crowns and bridges.
  • Being resistant to oxidation, thin layers of gold are electroplated on the exposed surfaces of electrical connectors to ensure good connections.
  • Gold performs critical functions in computers, communications equipment, jet aircraft engines, and a host of other products.
  • Being a good reflector of both infrared and visible light, gold is used for protective coatings on many artificial satellites.
  • Gold is used as a coating that enables biological material to be viewed under a scanning electron microscope.
  • The gold isotope Au-198 (half-life 2.7 days) is used as a treatment for cancer and other diseases.
  • Colloidal gold (containing nanoparticles of gold in suspension) is being studied in many labs for medical, biological, and other applications. It is also the form used as gold paint on ceramics prior to firing.
  • Chlorauric acid is used in photography for toning the silver image.
  • Gold (III) chloride is used as a catalyst in organic chemistry. It is also the usual starting point for making other gold compounds.
  • A gold compound known as disodium aurothiomalate is a treatment for rheumatoid arthritis, administered intramuscularly. It can, however, also cause photosensitive rashes, gastrointestinal disturbance, and kidney damage.
  • Gold flake is added to some gourmet sweets and drinks. Called varak (or varaq) in India, it has no reactivity and adds no taste but is taken as a delicacy. Some use it to create super-expensive cocktails.
  • White gold (an alloy of gold with platinum, palladium, nickel, and/or zinc) serves as a substitute for platinum.
  • Green gold and rose gold are alloys of gold with silver and copper, respectively, and are used in specialized jewelry.

It should be noted that the human body does not absorb gold very well. As a result, compounds of gold are normally not very toxic. In dentistry, gold is regarded as the safest and most successful form of restorative material. On the other hand, liver and kidney damage has been reported for up to 50 percent of arthritis patients treated with gold-containing drugs.

Production

The entrance to an underground gold mine in Victoria, Australia
Gold ore

According to some estimates, all the gold in the world that has ever been refined would form a single cube 20 meters (66 ft) on each side. About 75 percent of that has been extracted since 1910.

In large, easily mined deposits, economic gold extraction can be achieved from ore grades as low as 0.5 g/1000 kg (0.5 ppm), on average. Typical ore grades in open-pit mines are 1–5 g/1000 kg (1-5 ppm); ore grades in underground or hard rock mines are usually at least 3 g/1000 kg (3 ppm), on average. Ore grades of 30 g/1000 kg (30 ppm) are usually needed before gold is visible to the naked eye. Thus, in most gold mines you will not see any gold.

Extraction methods

In the past, prospectors found grains and lumps of gold along stream beds. They used the process of panning to separate the heavier gold pieces from the sand and gravel. Later, various techniques were developed to extract gold from the rocky vein or mother lode. Some of these are described below.

  • Gravity separation: The rock may be crushed into fine particles, mixed with water, and made to flow down a sloping trough. Gold, being heavier than other particles, gets lodged in riffles in the trough.
  • Amalgamation: Crushed rock is treated with mercury, which readily dissolves the gold to form a liquid alloy called an amalgam. The amalgam is separated from the rock and squeezing and heating remove the mercury. The gold is left behind.
  • Cyanide treatment: Certain cyanide compounds can be used to dissolve the gold and separate it from the rock. The gold can then be recovered by adding other chemicals to the solution.

The downside of gold extraction methods is that if they are not performed with extreme care, they can have harmful effects on the environment. On the one hand, open-pit mining operations tear up the landscape, which needs to be repaired later. On the other hand, chemical extraction techniques can leave residues of toxic chemicals in the environment. Mercury and cyanides are toxic substances, but mercury tends to linger and accumulate, while cyanides break down.

Gold extracted by the above methods is often alloyed with silver and other metals, and it needs to be refined. Mints in the United States use a process called electrolysis, which produces nearly pure gold.

Chemists have demonstrated the futility of the alchemist's dream of producing gold from other substances via chemical reactions. Interestingly, however, modern science has shown that it is feasible to generate minuscule amounts of gold by artificial nuclear transformations in particle accelerators. The product is likely to be one or more radioactive isotopes of gold.

The world's oceans hold a vast amount of gold, but at very low concentrations (perhaps 1-2 parts per billion). No commercially viable mechanism for extracting gold from seawater has yet been identified.

Gold-producing regions around the world

Since the 1880s, South Africa has accounted for a large proportion of the world's gold production. In 1970 South Africa's production of gold, about 1,000 tons, was 79 percent of the global total. By 2004, however, the country's production had fallen to 342 tons as a result of the increasing difficulty of extraction and changing economic factors affecting the industry in South Africa.

The city of Johannesburg was built atop the world's greatest gold finds. Gold fields in the Orange Free State and the Transvaal are deep and require the world's deepest mines. The Second Boer War of 1899–1901, between the British Empire and the white Boers, was at least partly over the rights of miners and possession of the gold wealth in South Africa. The Indian city of Kolar is also built on a great gold deposit.

Other major producers are Canada, the United States, and Australia. Mines in South Dakota and Nevada supply two-thirds of the gold used in the United States. The Siberian regions of Russia used to be significant in the global gold mining industry. In South America, the controversial project Pascua Lama aims at exploitation of rich fields in the high mountains of Atacama, at the border between Chile and Argentina.

Monetary value

Like other precious metals, gold is measured by troy weight or grams. When alloyed with other metals, the term carat (karat) is used to indicate the proportion of gold present. Pure gold is given the value 24 carats, and lower ratings correspond to proportionally less gold. The purity of a gold bar may also be expressed as a decimal figure ranging from 0 to 1, known as the millesimal fineness.

Price of gold

Gold bars with Krugerrands in the background.

The price of gold is determined on the open market, but a procedure known as the Gold Fixing in London, originating in 1919, provides a twice-daily benchmark figure to the industry.

Historically, gold was used to back currency in an economic system called the gold standard, in which one unit of currency was equivalent to a certain weight of gold. In this system, governments and central banks attempted to control the price of gold by setting values at which they would exchange it for currency. For a long period, the U.S. government set the price of gold at $20.67 per troy ounce ($664.56/kg), but in 1934, the price of gold was set at $35.00 per troy ounce ($1125.27/kg). By 1961, it was becoming hard to maintain this price, and a pool of U.S. and European banks began acting together to defend the price against market forces.

On March 17, 1968, economic circumstances led to 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 value of $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 banks still hold historical gold reserves as assets, although these levels have generally been declining. The largest gold depository in the world is that of the U.S. Federal Reserve Bank in New York.

Since 1968, the price of gold on the open market has ranged widely, with a record 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 Fixing). In late 2005, prices rose to the $500/oz mark, due to a depreciation of the U.S. dollar and inflation driven by rising energy costs.

Gold and the money supply

In January 1959, the U.S. M3 money supply (the broadest measure of money used by economists) was $288.8 billion, and the Official Gold Holdings of the United States was 17,335.1 tons, or 557 million ounces (there are 32,150.7 troy ounces in a ton). In other words, in 1959, there were $518 in circulation for every ounce of gold reserves held by the United States. The theoretical price should then have been $518 per ounce, but the actual price (fixed under the gold standard) was only $35 per ounce.

By August 2005, the U.S. M3 money supply had risen to $9,873.9 billion, while the Official Gold Holdings had fallen to just 8,133.5 tons, or about 261 million troy ounces. This means that in 2005, there were $37,831 in circulation for every ounce of gold held by the United States. These numbers show the falling influence of gold in the monetary system of the world.

Gold in investment portfolios

As a tangible investment, gold is sometimes held as part of a portfolio because it has an extensive history of maintaining its value over the long term. In the last century, it has gained ground in relation to fiat currencies owing to inflation. Gold becomes particularly desirable in times of extremely weak confidence and during hyperinflation because it maintains its value even as fiat money becomes worthless. People who enjoy investing in gold are known as gold bugs. Many of them believe, or even hope, that one day gold's importance will return as the printing of paper money gets out of control and we end in a hyper-inflationary fiat money collapse.

In some countries such as Switzerland, it is possible to hold physical gold as part of an investment portfolio. In other countries, however, portfolio managers may hold gold shares or gold bullion securities as proxies for the metal itself. Exchange-traded funds (ETFs), such as gold bullion securities, are sponsored by the World Gold Council and are fully backed by allocated gold held by a custodian.

Restrictions on gold ownership

Because of its use as a reserve store of value, the possession of gold is sometimes restricted or banned. Within the United States, the private possession of gold except as jewelry and coin collecting was banned between 1933 and 1975. President Franklin D. Roosevelt expropriated gold by Executive Order 6102, and President Richard Nixon closed the gold window by which foreign countries could exchange American dollars for gold at a fixed rate.

Controversies

In the twenty first century, gold is at the center of a swirling controversy over its uses and value in relation to the environmental costs of producing it. The two sides of the issue are finely drawn and both present persuasive arguments supporting their view. On the one side are environmentally conscious people, mostly from the developed countries, who point both to the high environmental costs of gold mining, including huge volumes of water consumed and landscapes chewed up and contaminated with cyanide or mercury and the fact that the largest single use of gold is for gold jewelry. On the other side are representatives of the gold mining industry who point to the very significant economic benefits to the countries hosting the gold mining operations and point out that in many developing countries with high inflation rates gold is perhaps the most reliable form of wealth. They further point out that in much of India gold jewelry is the only form of wealth that many woman traditionally could own, so the jewelry is much more than a vanity possession, it is an essential element for a woman's financial security.

With its many special properties and deep ties to financial markets, greed, high technology, environmental desecration, beauty, vanity, and, for some of the lesser developed countries, development, education, and economic security, gold in many ways embodies the best and the worst of humanity. In the coming decades the fate of gold may well be seen as a monitor of the progress of humanity toward a peaceful, happy world.

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