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'''Gold''' ({{IPAc-en|icon|ˈ|ɡ|oʊ|l|d}}) is a [[chemical element]] with the symbol '''Au''' (from {{lang-la|[[:wikt:aurum|aurum]]}} "gold") and an [[atomic number]] 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]] and a [[group 11 element]]. It is one of the least reactive solid chemical elements. The metal therefore occurs often in free elemental (native) form, as [[gold nugget|nuggets]] or grains in rocks, in [[vein (geology)|veins]] and in [[alluvial deposit]]s. 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]] (nitro-hydrochloric acid), so named because it dissolves gold. Gold also dissolves in alkaline solutions of [[cyanide]], which have been used in mining. Gold dissolves in [[mercury (element)|mercury]], forming [[amalgam (chemistry)|amalgam]] alloys. Gold is insoluble in [[nitric acid]], which dissolves [[silver]] and [[base metal]]s, a property that has long been used to confirm the presence of gold in items, giving rise to the term ''the [[acid test (gold)|acid test]].''

Gold has been a valuable and highly sought-after [[precious metal]] for [[coin]]age, jewelry, and other arts since long before the beginning of [[recorded history]]. [[Gold standard]]s have been the most common basis for [[monetary policy|monetary policies]] 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]]s of gold have been mined in human history, as of 2009.<ref name="World Gold Council FAQ">[http://www.gold.org/faq/answer/76/how_much_gold_has_been_mined/ World Gold Council FAQ]</ref> This is roughly equivalent to 5.3 billion [[troy ounce]]s or, in terms of volume, about 8500 m<sup>3</sup>, or a [[cube]] 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.<ref name='oil-price.com-worlds-gold-consumption 2011'>{{cite news|first = Andy |last = Soos|title = Gold Mining Boom Increasing Mercury Pollution Risk|date = 2011-01-06|publisher = Oilprice.com|url = http://oilprice.com/Metals/Gold/Gold-Mining-Boom-Increasing-Mercury-Pollution-Risk.html|work = Advanced Media Solutions, Inc.|accessdate = 2011-03-26}}</ref>

Besides its widespread monetary and symbolic functions, gold has many practical uses in [[dentistry]], [[electronics]], and other fields. Its high [[malleability]], [[ductility]], 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]] eating.

==Characteristics==
Gold is the most [[malleable]] and [[ductility|ductile]] of all metals; a single gram can be beaten into a sheet of 1 square meter, or an [[ounce]] into 300 square feet. Gold leaf can be beaten thin enough to become transparent. The transmitted light appears greenish blue, because gold strongly reflects yellow and red.<ref>{{Cite web|url = http://www.webexhibits.org/causesofcolor/9.html|title=Gold: causes of color|accessdate=2009-06-06}}</ref> 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 [[spacesuit]]s.<ref>{{Cite book|title=Suiting up for space: the evolution of the space suit|last=Mallan|first=Lloyd|year=1971|publisher=John Day Co|isbn=978-0381981501|page=216}}</ref>

Gold readily creates [[alloy]]s with many other metals. These alloys can be produced to modify the hardness and other metallurgical properties, to control [[melting point]] or to create exotic colors (see below).<ref name=coloredgold/> Gold is a good [[conduction (heat)|conductor of heat]] and [[Electrical conductor|electricity]] and reflects [[infrared radiation]] strongly. Chemically, it is unaffected by [[Earth's atmosphere|air]], [[moisture]] and most [[corrosion|corrosive]] [[reagent]]s, and is therefore well suited for use in [[coin]]s and [[jewelry]] and as a protective coating on other, more reactive, metals. However, it is not chemically inert.

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 adding 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.

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).<ref>{{Cite book|url=http://books.google.com/?id=C8UHAAAAIAAJ&pg=PA280|page=280|title=General notions of chemistry|author=Pelouze, Jules and Fremy, Edmond|publisher=Lippincott, Grambo & Co.|year=1854}}</ref>

In addition, gold is very dense, a cubic meter weighing 19,300 [[kilograms|kg]]. By comparison, the density of [[lead]] is 11,340&nbsp;kg/m<sup>3</sup>, and that of the densest element, [[osmium]], is 22,610&nbsp;kg/m<sup>3</sup>.

===Color===
[[File:Ag-Au-Cu-colours-english.svg|thumb|left|Different colors of Ag-Au-Cu alloys]]
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]] called [[plasmon]]. 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 quantum chemistry|relativistic effects]] that affect the [[atomic orbital|orbitals]] around gold atoms.<ref>{{Cite web|url=http://math.ucr.edu/home/baez/physics/Relativity/SR/gold_color.html|title=Relativity in Chemistry|publisher=Math.ucr.edu|accessdate=2009-04-05}}</ref><ref>{{Cite journal|journal = Chemical Physics|volume = 311|pages = 151–161|title = Understanding gold chemistry through relativity|doi = 10.1016/j.chemphys.2004.09.023|first = Hubert|last = Schmidbaur|coauthors = Cronje, Stephanie; Djordjevic, Bratislav; Schuster, Oliver|year = 2005|issue = 1–2|bibcode = 2005CP....311..151S }}</ref> Similar effects impart a golden hue to metallic [[caesium]] (see [[relativistic quantum chemistry]]).

Common [[colored gold]] 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]], [[aluminium]], [[iron]], [[indium]] and other elements can produce more unusual colors of gold for various applications.<ref name=coloredgold>{{Cite web|url=http://www.utilisegold.com/jewellery_technology/colours/colour_alloys/|title=Gold Jewellery Alloys > Utilise Gold. Scientific, industrial and medical applications, products, suppliers from the World Gold Council|publisher=Utilisegold.com|date=2000-01-20|accessdate=2009-04-05}}</ref>

===Isotopes===
{{Main|Isotopes of gold}}
Gold has only one stable [[isotope]], <sup>197</sup>Au, which is also its only naturally occurring isotope. Thirty-six [[radioisotopes]] have been synthesized ranging in [[atomic mass]] from 169 to 205. The most stable of these is <sup>195</sup>Au with a [[half-life]] of 186.1 days. The least stable is <sup>171</sup>Au, which decays by [[proton emission]] with a half-life of 30 µs. Most of gold's radioisotopes with atomic masses below 197 decay by some combination of [[proton emission]], [[alpha decay|α decay]], and [[Beta decay#β+ decay|β+ decay]]. The exceptions are <sup>195</sup>Au, which decays by electron capture, and <sup>196</sup>Au, which decays most often by electron capture (93%) with a minor [[Beta decay#β− decay|β- decay]] path (7%).<ref>[http://www.nndc.bnl.gov/nudat2/ National Nuclear Data Center Nudat 2]</ref> All of gold's radioisotopes with atomic masses above 197 decay by β- decay.<ref name="nubase">{{Cite journal|author = Audi, G.|title = The NUBASE Evaluation of Nuclear and Decay Properties|journal = Nuclear Physics A|volume = 729|pages = 3–128|publisher = Atomic Mass Data Center|year = 2003|doi = 10.1016/j.nuclphysa.2003.11.001|bibcode=2003NuPhA.729....3A}}</ref>

At least 32 [[nuclear isomer]]s have also been characterized, ranging in atomic mass from 170 to 200. Within that range, only <sup>178</sup>Au, <sup>180</sup>Au, <sup>181</sup>Au, <sup>182</sup>Au, and <sup>188</sup>Au do not have isomers. Gold's most stable isomer is <sup>198m2</sup>Au with a half-life of 2.27 days. Gold's least stable isomer is <sup>177 m2</sup>Au with a half-life of only 7 ns. <sup>184 m1</sup>Au has three decay paths: β+ decay, [[isomeric transition]], and alpha decay. No other isomer or isotope of gold has three decay paths.<ref name="nubase"/>

==Use and applications==
===Monetary exchange===
Gold has been widely used throughout the world as a [[vehicle]] for [[money|monetary]] exchange, either by issuance and recognition of [[gold coin]]s or other bare metal quantities, or through gold-convertible paper instruments by establishing [[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]] output is declining.<ref>{{Cite web|url=http://goldnews.bullionvault.com/gold_mine_production_072020092|title=Gold mining decline|author=King, Byron|publisher= BullionVault.com|date=2009-07-20|accessdate=2009-11-23}}</ref> With the sharp growth of economies in the 20th century, and increasing foreign exchange, the world's [[gold reserve]]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]] the warring nations moved to a fractional gold standard, inflating their currencies to finance the war effort. After [[World War II]] gold was replaced by a system of [[convertible currency]] following the [[Bretton Woods system]]. [[Gold standard]]s and the direct convertibility of currencies to gold have been abandoned by world governments, being replaced by [[fiat currency]] in their stead. [[Switzerland]] was the last country to tie its currency to gold; it backed 40% of its value until the Swiss joined the [[International Monetary Fund]] in 1999.<ref>{{cite news| url=http://www.nytimes.com/1999/04/19/world/swiss-narrowly-vote-to-drop-gold-standard.html | work=The New York Times | title=Swiss Narrowly Vote to Drop Gold Standard | date=1999-04-19}}</ref>

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 [[carat (purity)|carats]] (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]], for hardness (American gold coins for circulation after 1837 contained the slightly lower amount of 0.900 fine gold, or 21.6 kt).

===Investment===
{{Main|Gold as an investment}}
[[File:Gold Spot Price per Gram from Jan 1971 to Jan 2012.svg|thumb|300px|Gold Price per gram between Jan 1971 and Jan 2012. The graph shows nominal price in US Dollars, the price in 1971 and 2011 US Dollars]]

Many holders of gold store it in form of bullion coins or [[gold bar|bar]]s as a hedge against [[inflation]] or other economic disruptions. However, some economists do not believe gold serves as a hedge against inflation or currency depreciation.<ref>{{Cite web|url=http://host.madison.com/ct/news/opinion/column/article_68f99b80-4258-5f44-a817-5cc64c6e1884.html|title=Is Gold a Good Hedge?|author=Martin Feldstein|publisher=Project Syndicate|date=2009-12-26|accessdate=2009-12-29}}</ref>

The [[ISO 4217]] currency code of gold is XAU.

Modern [[bullion coin]]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]], the British [[Sovereign (British coin)|gold sovereign]], and the [[South Africa]]n [[Krugerrand]] continue to be minted in 22k metal in historical tradition. The ''special issue'' [[Canadian Gold Maple Leaf]] coin contains the highest purity gold of any [[bullion coin]], at 99.999% or 0.99999, while the ''popular issue'' Canadian Gold Maple Leaf coin has a purity of 99.99%. 

Several other 99.99% pure gold coins are available. In 2006, the [[United States Mint]] began production of the [[American Buffalo (coin)|American Buffalo]] gold bullion coin with a purity of 99.99%. The [[Australia]]n Gold Kangaroos were first coined in 1986 as the [[Australian Gold Nugget]] but changed the reverse design in 1989. Other popular modern coins include the [[Austria]]n [[Euro gold and silver commemorative coins (Austria)#Vienna Philharmonic Coin|Vienna Philharmonic bullion coin]] and the [[Chinese Gold Panda]].

===Jewelry===
{{Main|Jewellery}}
[[File:MocheGoldNecklace.jpg|thumb|[[Moche]] gold necklace depicting feline heads. [[Larco Museum]] Collection. Lima-Peru]]
Because of the softness of pure (24k) gold, it is usually [[alloy]]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]] is the most commonly used base metal, yielding a redder color.<ref name="utilisegold">World Gold Council, Jewellery Technology, [http://www.utilisegold.com/jewellery_technology/colours/colour_alloys/ Jewellery Alloys]</ref>

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]] alloys, and both may be used to produce police and other [[badge]]s. Blue gold can be made by alloying with [[iron]] and purple gold can be made by alloying with [[aluminium]], although rarely done except in specialized jewelry. Blue gold is more brittle and therefore more difficult to work with when making jewelry.<ref name="utilisegold" />

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]] or [[nickel]]. 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.<ref name="utilisegold" />

Alternative [[white gold]] alloys are available based on palladium, silver and other white metals,<ref name="utilisegold" /> 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]]. The Japanese craft of [[Mokume-gane]] 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 [[esotericism|esotericists]] and forms of [[alternative medicine]] assign metallic gold a healing power.<ref>{{Cite web|url = http://health.ninemsn.com.au/article.aspx?id=694367|title=The healing power of precious metals|accessdate= 2009-06-06}}</ref> Some gold salts do have [[anti-inflammatory]] properties and are used as pharmaceuticals in the treatment of arthritis and other similar conditions.<ref name="Messorri">{{Cite book|url=http://books.google.com/?id=wgifUs8dFbgC&pg=PA279|chapter=Gold Complexes in the treatment of Rheumatoid Arthritis|first=L.|last=Messori|coauthor=Marcon, G.|title=Metal ions and their complexes in medication|editor=Sigel, Astrid|publisher=CRC Press|year=2004|isbn=9780824753511|pages= 280–301}}</ref> Gold based injections have been explored as a means to help to reduce the pain and swelling of [[rheumatoid arthritis]] and [[tuberculosis]].<ref name="Messorri"/><ref>{{Cite web|url= http://besthealth.bmj.com/btuk/conditions/14212.html|title=BMJ: '&#39;login required'&#39;|publisher=Besthealth.bmj.com|accessdate = 2009-04-05}} {{Dead link|date=October 2010|bot=H3llBot}}</ref> 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.

Gold alloys are used in [[restorative dentistry]], especially in tooth restorations, such as [[crown (dentistry)|crowns]] and permanent [[bridge (dentistry)|bridges]]. The gold alloys' slight malleability facilitates the creation of a superior molar mating surface with other teeth and produces results that are generally more satisfactory than those produced by the creation of porcelain crowns. The use of gold crowns in more prominent teeth such as incisors is favored in some cultures and discouraged in others.

[[Colloidal gold]] preparations (suspensions of gold [[nanoparticles]]) in water are intensely red-[[color]]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]] or [[ascorbate]] ions. Colloidal gold is used in research applications in medicine, biology and [[materials science]]. The technique of [[immunogold labeling]] exploits the ability of the gold particles to adsorb protein molecules onto their surfaces. Colloidal gold particles coated with specific antibodies can be used as probes for the presence and position of antigens on the surfaces of cells.<ref>{{Cite journal|doi=10.1016/0019-2791(71)90496-4|pmid=4110101|year=1971|last1=Faulk|first1=WP|last2=Taylor|first2= GM|title=An immunocolloid method for the electron microscope|volume=8|issue=11|pages=1081–3|journal=Immunochemistry}}</ref> In ultrathin sections of tissues viewed by [[electron microscope|electron microscopy]], the immunogold labels appear as extremely dense round spots at the position of the [[antigen]].<ref>{{Cite journal|pmid=6153194|url=http://www.jhc.org/cgi/reprint/28/1/55.pdf|year=1980|last1=Roth|first1=J|last2=Bendayan|first2=M|last3=Orci|first3=L|title=FITC-protein A-gold complex for light and electron microscopic immunocytochemistry|volume=28|issue=1|pages=55–7|journal=The journal of histochemistry and cytochemistry : official journal of the Histochemistry Society|doi=10.1177/28.1.6153194}}</ref> 

Gold, or alloys of gold and [[palladium]], are applied as conductive coating to biological specimens and other non-conducting materials such as plastics and glass to be viewed in a [[scanning electron microscope]]. The coating, which is usually applied by [[sputtering]] with an [[argon]] [[plasma (physics)|plasma]], has a triple role in this application. Gold's very high electrical conductivity drains [[electric charge|electrical charge]] to earth, and its very high density provides stopping power for electrons in the [[electron beam]], helping to limit the depth to which the electron beam penetrates the specimen. This improves definition of the position and topography of the specimen surface and increases the [[Angular resolution|spatial resolution]] of the image. Gold also produces a high output of [[secondary emission|secondary electrons]] when irradiated by an electron beam, and these low-energy electrons are the most commonly used signal source used in the scanning electron microscope.<ref>{{Cite book|url= http://books.google.com/?id=RqSMzR-IXk0C&pg=PA65|page=65|title=Electron microscopy: principles and techniques for biologists|author=Bozzola, John J. and Russell, Lonnie Dee|publisher=Jones & Bartlett Learning|year=1999|isbn=0763701920}}</ref>

The isotope gold-198, ([[half-life]] 2.7 days) is used in some [[cancer]] treatments and for treating other diseases.<ref>[http://web.missouri.edu/~kattik/katti/katres.html Nanoscience and Nanotechnology in Nanomedicine: Hybrid Nanoparticles In Imaging and Therapy of Prostate Cancer] – Radiopharmaceutical Sciences Institute, University of Missouri-Columbia</ref>

===Food and drink===
*Gold can be used in food and has the [[E number]] 175.<ref name=FSA>{{Cite news|url=http://www.food.gov.uk/safereating/chemsafe/additivesbranch/enumberlist|title=Current EU approved additives and their E Numbers|date=27 July 2007|publisher=Food Standards Agency, UK}}</ref>
*[[Gold leaf]], flake or dust is used on and in some gourmet foods, notably sweets and drinks as decorative ingredient.<ref>{{Cite web|title=The Food Dictionary: Varak|publisher=Barron's Educational Services, Inc|year=1995|url=http://www.epicurious.com/cooking/how_to/food_dictionary/entry?id=5061|accessdate=2007-05-27}}</ref> 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]] ({{lang-en|Goldwater}}) is a traditional German herbal [[liqueur]]<ref>{{Cite book|url=http://books.google.com/?id=tsUNAAAAYAAJ&pg=PA101|title=Deutschland nebst Theilen der angrenzenden Länder|chapter=Danzig|first=Karl|last=Baedeker|year=1865|publisher=Karl Baedeker|language=German}}</ref> produced in what is today [[Gdańsk]], [[Poland]], and [[Schwabach]], Germany, and contains flakes of gold leaf. There are also some expensive (~$1000) cocktails which contain flakes of gold leaf.<ref>Guinness Book of World Records 2008</ref> However, since metallic gold is inert to all body chemistry, it has no taste, it provides no nutrition, and it leaves the body unaltered.<ref>{{Cite web|url=http://geology.com/minerals/gold/uses-of-gold.shtml|title=The Many Uses of Gold|accessdate=2009-06-06}}</ref>

===Industry===
[[File:220kg Gold brick Taiwan Museum.jpg|thumb|The 220 kg gold brick displayed in [[Jinguashi]] Gold Museum, [[Taiwan Province|Taiwan]], [[Republic of China]].]]
[[File:Toi 250kg gold bar.jpg|upright|thumb|The [[world's largest gold bar]] has a mass of 250 kg. [[Toi gold mine|Toi museum]], [[Japan]].]]
[[File:Small gold nugget 5mm dia and corresponding foil surface of half sq meter.jpg|upright|thumb|A gold nugget of 5 mm in diameter (bottom) can be expanded through hammering into a [[gold foil]] of about 0.5 square meter. [[Toi gold mine|Toi museum]], [[Japan]].]]

*Gold [[solder]] is used for joining the components of gold jewelry by high-temperature hard soldering or [[brazing]]. If the work is to be of [[hallmark]]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 [[gold thread|thread]] and used in [[embroidery]].
*Gold produces a deep, intense red color when used as a coloring agent in [[cranberry glass]].
*In photography, gold toners are used to shift the color of [[silver bromide]] black-and-white prints towards brown or blue tones, or to increase their stability. Used on [[sepia tone|sepia-toned]] prints, gold toners produce red tones. Kodak published formulas for several types of gold toners, which use gold as the chloride.<ref>Kodak (2006) [http://www.kodak.com/global/en/professional/support/techPubs/g23/g23.pdf Toning black-and-white materials]. Technical Data/Reference sheet G-23, May 2006.</ref>
*As gold is a good reflector of [[electromagnetic radiation]] such as infrared and [[visible spectrum|visible light]] as well as [[radio frequency|radio waves]], it is used for the protective coatings on many artificial [[satellite]]s, in infrared protective faceplates in thermal protection suits and astronauts' helmets and in [[electronic warfare]] planes like the [[EA-6B Prowler]].
*Gold is used as the reflective layer on some [[Gold CD|high-end CDs]].
*Automobiles may use gold for heat dissipation. [[McLaren]] uses gold foil in the engine compartment of its [[McLaren F1|F1]] model.<ref>Super cars.net. [http://www.supercars.net/cars/1177.html 1994 McLaren F1]</ref>
*Gold can be manufactured so thin that it appears transparent. It is used in some aircraft cockpit windows for [[Deicing|de-icing]] or anti-icing by passing electricity through it. The heat produced by the resistance of the gold is enough to deter ice from forming.<ref name=gbc215>{{Cite news|url = http://www.goldbulletin.org/assets/file/goldbulletin/downloads/Cooke_2_15.pdf|title = The Demand for Gold by Industry|publisher = Gold bulletin|accessdate = 2009-06-06}}</ref>

===Electronics===
The concentration of free electrons in gold metal is 5.90×10<sup>22</sup> cm<sup>−3</sup>. Gold is highly [[electrical conductivity|conductive]] to electricity, and has been used for [[electrical wiring]] in some high-energy applications (only silver and copper are more conductive per volume, but gold has the advantage of corrosion resistance). For example, gold electrical wires were used during some of the [[Manhattan Project]]'s atomic experiments, but large high current silver wires were used in the [[calutron]] isotope separator magnets in the project.

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]]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]] 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]]s, communications equipment, [[spacecraft]], [[jet aircraft]] engines) remains very common.<ref>{{Cite book|url=http://books.google.com/?id=G7JrhAy5phoC&pg=PA597|page=597|title=Encyclopedia of world environmental history, Volume 3|author=Krech, Shepard; McNeill, John Robert and Merchant, Carolyn|publisher=Routledge|year=2004|isbn=0415937345}}</ref>

Besides sliding electrical contacts, gold is also used in [[Switch#Contacts|electrical contacts]] because of its resistance to [[corrosion]], [[electrical conductivity]], [[ductile|ductility]] and lack of [[toxicity]].<ref>{{Cite web|title=General Electric Contact Materials|work=Electrical Contact Catalog (Material Catalog)|publisher=Tanaka Precious Metals|year=2005|url= http://www.tanaka-precious.com/catalog/material.html|accessdate=2007-02-21}}</ref> Switch contacts are generally subjected to more intense corrosion stress than are sliding contacts. Fine gold wires are used to connect [[semiconductor device]]s to their packages through a process known as [[wire bonding]].

===Commercial chemistry===
Gold is attacked by and dissolves in alkaline solutions of potassium or sodium [[cyanide]], to form the salt gold cyanide—a technique that has been used in extracting metallic gold from ores in the [[cyanide process]]. Gold cyanide is the [[electrolyte]] used in commercial [[electroplating]] of gold onto base metals and [[electroforming]].

Gold chloride ([[chloroauric acid]]) solutions are used to make colloidal gold by reduction with [[citrate]] or [[ascorbate]] [[ions]]. Gold chloride and gold oxide are used to make highly valued cranberry or red-colored glass, which, like [[colloid]]al gold suspensions, contains evenly sized spherical gold [[nanoparticle]]s.<ref>{{Cite web|url = http://chemistry.about.com/cs/inorganic/a/aa032503a.htm|title= Colored glass chemistry|accessdate=2009-06-06}}</ref>

==History==
[[File:TurinPapyrus1.jpg|thumb|The [[Turin Papyrus Map]]]]
[[File:Tuthankhamun Egyptian Museum.jpg|thumb|upright|[[Funerary art|Funerary mask]] of [[Tutankhamun]]]]
[[File:Jason Pelias Louvre K127.jpg|thumb|upright|[[Jason]] returns with the golden fleece on an [[Apulia]]n [[Red-figure pottery|red-figure]] [[krater|calyx krater]], ca. 340–330 BC.]]

Gold artifacts found at the Nahal Kana cave cemetary dated during  the 1980's, showed these to be from within the [[Chalcolithic]], and considered the earliest find from the Levant (Gopher et al 1990). <ref name=" Gopher, Tsuk,  Shalev and  Gophna"> {{cite article |url=http://www.jstor.org/stable/2743275 |author=A. Gopher, T. Tsuk, S. Shalev and R. Gophna (Institute of Archaeology, Tel Aviv University) |title=Earliest Gold Artifacts in the Levant | year=(Aug. - Oct., 1990) |publisher=The University of Chicago Press| retrieved=}}</ref> Gold artifacts in the [[Balkans]] also appear from the 4th millennium BC, such as those found in the [[Varna Necropolis]] near  Lake Varna in  [[Bulgaria]], thought by one source (La Niece 2009) to be the earliest "well-dated" find of gold artifacts. <ref name=" La Niece "> {{cite book |url=http://books.google.co.uk/books?id=oAfITjcHiZ0C&printsec=frontcover&dq=gold&hl=en&sa=X&ei=0B2ET62-I8rB0QWj2JDDBw&ved=0CFoQ6AEwBQ#v=onepage&q=gold&f=false |author=Susan La Niece (senior metallurgist in the British Museum Department of Conservation and Scientific Research)  |title=Gold (p.10) | year= |publisher=Harvard University Press, 15 Dec 2009| retrieved=2012-04-10|isbn= 0674035909}}</ref> Gold artifacts such as the [[golden hats]] and the [[Nebra disk]] appeared in Central Europe from the 2nd millennium BC [[European Bronze Age|Bronze Age]].

[[Egyptian hieroglyph]]s from as early as 2600 BC describe gold, which king [[Tushratta]] of the [[Mitanni]] claimed was "more plentiful than dirt" in Egypt.<ref>Reeves, Nicholas ''Akhenaten: Egypt's False Prophet'', Thames & Hudson, p.69 ISBN 0500285527</ref> Egypt and especially [[Nubia]] 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]] and shows the plan of a [[gold mine]] in Nubia together with indications of the local [[geology]]. The primitive working methods are described by both [[Strabo]] and [[Diodorus Siculus]], and included [[fire-setting]]. Large mines were also present across the [[Red Sea]] in what is now [[Saudi Arabia]].

The legend of the [[golden fleece]] may refer to the use of fleeces to trap gold dust from [[placer deposit]]s in the ancient world. Gold is mentioned frequently in the [[Old Testament]], starting with [[Book of Genesis|Genesis]] 2:11 (at [[Havilah]]) and is included with the gifts of the [[magi]] in the first chapters of Matthew [[New Testament]]. The [[Book of Revelation]] 21:21 describes the city of [[New Jerusalem]] as having streets "made of pure gold, clear as crystal". The south-east 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 is probably the world's earliest coinage in [[Lydia]] around 610 BC.<ref>{{Cite web|url = http://rg.ancients.info/lion/article.html|title = A Case for the World's First Coin: The Lydian Lion|accessdate = 2009-07-24}}</ref> From the 6th or 5th century BC, the [[Chu (state)]] circulated the [[Ying Yuan]], one kind of square gold coin.

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

The [[Mali Empire]] in Africa was famed throughout the [[Old World|old world]] for its large amounts of gold. [[Mansa Musa]], ruler of the empire (1312–1337) became famous throughout the old world for his great [[hajj]] to [[Mecca]] in 1324. When he passed through [[Cairo]] in July 1324, he was reportedly accompanied by a [[camel train]] 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.<ref>[http://blackhistorypages.net/pages/mansamusa.php Mansa Musa] – Black History Pages</ref> A contemporary Arab historian remarked:

{{quote|Gold was at a high price in Egypt until they came in that year. The mithqal did not go below 25 dirhams and was generally above, but from that time its value fell and it cheapened in price and has remained cheap till now. The mithqal does not exceed 22 dirhams or less. This has been the state of affairs for about twelve years until this day by reason of the large amount of gold which they brought into Egypt and spent there [...]|[[Chihab Al-Umari]]<ref>{{Cite web|title=Kingdom of Mali – Primary Source Documents|url=http://www.bu.edu/africa/outreach/resources/k_o_mali/|work=African studies Center|publisher=[[Boston University]]|accessdate=2012-01-30}}</ref>}}

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]], [[Ecuador]] and [[Colombia]]. The [[Aztec]]s regarded gold as literally the product of the gods, calling it "god excrement" (''teocuitlatl'' in [[Nahuatl]]).<ref>{{Cite book|author1=Berdan, Frances|author2=Anawalt, Patricia Rieff|title=The Codex Mendoza|volume=2|page= 151|publisher=[[University of California Press]]|year=1992|isbn=9780520062344}}</ref> However, for the [[indigenous peoples]] of [[North America]],  gold was considered useless, and they saw much greater value in other [[minerals]], which were directly related to their utility, such as [[obsidian]], [[flint]], and [[slate]].<ref>[http://www.sierranevadavirtualmuseum.com/docs/galleries/history/culture/shadows.htm Sierra Nevada Virtual Museum]</ref>

Although the price of some [[platinum]] group metals can be much higher, gold has long been considered the most desirable of [[precious metal]]s, and its value has been used as the standard for many [[currency|currencies]] (known as the [[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]] in his treatise [[Utopia (book)|''Utopia'']]. On that imaginary island, gold is so abundant that it is used to make chains for slaves, tableware and lavatory-seats. When ambassadors from other countries arrive, dressed in ostentatious gold jewels and badges, the Utopians mistake them for menial servants, paying homage instead to the most modestly dressed of their party.

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]] if sufficient lead is absorbed by the biting).

Gold in antiquity was relatively easy to obtain [[geology|geologically]]; however, 75% of all gold ever produced has been extracted since 1910.<ref name="goldsheetlinks">{{Cite web|url=http://www.goldsheetlinks.com/production2.htm|title=Goldsheet – yearly and cumulative world gold production charts|accessdate=2006-07-22}}</ref> It has been estimated that all gold ever refined would form a single cube 20&nbsp;m (66&nbsp;ft) on a side (equivalent to 8,000 m<sup>3</sup>).<ref name="goldsheetlinks"/>

One main goal of the [[alchemy|alchemists]] was to produce gold from other substances, such as [[lead]] — 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]] (☉), which was also the [[astrology|astrological]] symbol and the ancient [[Chinese character]] for the [[Sun]]. For modern creation of artificial gold by [[neutron capture]], see [[Synthesis of noble metals#Gold|gold synthesis]].

During the 19th century, [[gold rush]]es occurred whenever large gold deposits were discovered. The first documented discovery of gold in the United States was at the [[Reed Gold Mine]] near Georgeville, North Carolina in 1803.<ref>{{Cite web|url= http://www.nchistoricsites.org/Reed/reed.htm|title=Reed Gold Mine State Historic Site|last=Moore|first=Mark A.|year=2006|publisher = North Carolina Office of Archives and History|accessdate=2008-12-13}}</ref> The first major gold strike in the United States occurred in a small north Georgia town called [[Dahlonega, Georgia|Dahlonega]].<ref>{{Cite web|title=Road to adventure|publisher= Georgia Magazine|last=Garvey|first = Jane A.|url=http://www.georgiamagazine.org/archives_view.asp?mon=7&yr=2006&ID=1344|year= 2006 |accessdate=2007-01-23}}</ref> Further gold rushes occurred in [[California Gold Rush|California]], [[Pike's Peak Gold Rush|Colorado]], the [[Black Hills Gold Rush|Black Hills]], [[Central Otago Gold Rush|Otago]] in [[New Zealand]], [[Australian gold rushes|Australia]], [[Witwatersrand Gold Rush|Witwatersrand]] in [[South Africa]], and the [[Klondike Gold Rush|Klondike]] in [[Canada]].

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

==Occurrence==
[[File:Stringer156 nugget.jpg|thumb|This 156-ounce (4.85 kg) [[Gold nugget|nugget]] was found by an individual prospector in the Southern California Desert using a metal detector.]]

Gold's [[atomic number]] of 79 makes it one of the higher [[atomic number]] elements which occur naturally. Like all elements with atomic numbers larger than [[iron]], gold is thought to have been formed from a [[supernova nucleosynthesis]] process. Their explosions scattered metal-containing dusts (including [[Heavy metal (chemistry)|heavy elements]] like gold) into the region of space in which they later condensed into our [[solar system]] and the Earth.<ref>{{Cite journal|doi=10.1086/190111|title= Nucleosynthesis of Heavy Elements by Neutron Capture|year=1965|last1=Seeger|first1=Philip A.|last2=Fowler|first2=William A.|last3 = Clayton|first3=Donald D.|journal=The Astrophysical Journal Supplement Series|volume=11|pages=121|bibcode=1965ApJS...11..121S}}</ref> 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]].<ref>M. Willbold, T. Elliott and S. Moorbath, ''The tungsten isotopic composition of the Earth’s mantle before the terminal bombardment'', Nature '''477''', 195–198 (2011)</ref> 

On Earth, whenever elemental gold occurs, it appears most often as a metal [[solid solution]] of gold with silver, i.e. a [[gold silver alloy]]. Such alloys usually have a silver content of 8–10%. [[Electrum]] 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]].

[[File:Gold 30g for a 860kg rock.jpg|thumb|Relative sizes of an 860 kg block of gold ore, and the 30 g of gold that can be extracted from it. [[Toi gold mine]], [[Japan]].]]
[[File:GoldinPyriteDrainage acide.JPG|thumb|Gold left behind after a [[pyrite]] cube was oxidized to [[hematite]]. Note cubic shape of cavity.]]
Gold is found in [[ore]]s in rock formed from the Precambrian time onward. <ref name=" La Niece "/>  Sometimes occuring as very small to microscopic particles, this  ore is often found together with [[quartz]] or [[sulfide mineral]]s such as ''Fool's Gold'', which is a [[pyrite]].<ref>{{Cite web|url= http://arizonagoldprospectors.com/formation.htm|title=Formation of Lode Gold Deposits|publisher= arizonagoldprospectors.com| accessdate = 2009-05-23}}</ref> These are called [[lode]] deposits. The metal in a native state is also found in the form of free flakes, grains or larger [[Gold nugget|nugget]]s <ref name=" La Niece "/> that have been eroded from rocks and end up in [[alluvial]] deposits (called [[placer deposit]]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 [[Gold nugget|nugget]]s.

Gold sometimes occurs combined with [[tellurium]] as the [[mineral]]s [[calaverite]], [[krennerite]], [[nagyagite]], [[petzite]] and [[sylvanite]], and as the rare bismuthide [[maldonite]] (Au<sub>2</sub>Bi) and antimonide [[aurostibite]] (AuSb<sub>2</sub>). Gold also occurs in rare alloys with [[copper]], [[lead]], and [[mercury (element)|mercury]]: the minerals [[auricupride]] (Cu<sub>3</sub>Au), [[novodneprite]] (AuPb<sub>3</sub>) and [[weishanite]] ((Au, Ag)<sub>3</sub>Hg<sub>2</sub>).

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.<ref>{{Cite web|url=http://www.abc.net.au/science/news/enviro/EnviroRepublish_1032376.htm|title=Environment & Nature News – Bugs grow gold that looks like coral – 28 January 2004|accessdate=2006-07-22}} This is doctoral research undertaken by Frank Reith at the Australian National University, published 2004.</ref>

The world's [[ocean]]s contain gold. Measured concentrations of gold in the Atlantic and Northeast Pacific are 50–150 fmol/L or 10–30 parts per [[1,000,000,000,000,000|quadrillion]] (about 10–30 g/km<sup>3</sup>). 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.<ref>{{Cite journal|doi=10.1016/0012-821X(90)90060-B|title=Gold in seawater|first=K.|last=Kenison Falkner|journal= Earth and Planetary Science Letters|volume=98|year=1990|pages=208–221|last2=Edmond|first2=J|issue=2|bibcode=1990E&PSL..98..208K}}</ref> 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]] in the 1890s. A British fraudster ran the same scam in [[England]] in the early 1900s.<ref>Plazak, Dan ''A Hole in the Ground with a Liar at the Top'' (Salt Lake: Univ. of Utah Press, 2006) ISBN 0874808405 (contains a chapter on gold-from seawater swindles)</ref> [[Fritz Haber]] (the German inventor of the [[Haber process]]) did research on the extraction of gold from sea water in an effort to help pay [[Germany]]'s reparations following [[World War I]].<ref>{{Cite journal|title=Das Gold im Meerwasser|first=F.|last= Haber|volume=40|issue=11|year=1927|doi=10.1002/ange.19270401103|pages=303–314|journal=Zeitschrift für Angewandte Chemie}}</ref> 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.<ref>{{Cite journal|doi=10.1016/0375-6742(88)90051-9|title = Concentration of gold in natural waters|first= J.B.|last = McHugh|journal = Journal of Geochemical Exploration|volume = 30|year = 1988|pages = 85–94|issue = 1–3}}</ref><!--10.1007/BF01497020--> 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.

</center>

===Gallery of specimens of crystalline native gold===
<gallery heights="160px" widths="160px" perrow="5">
File:Native gold nuggets.jpg|Native [[gold nugget]]s
File:Gold-tt48a.jpg|"Rope gold" from [[Lena River]], [[Sakha Republic]], Russia. Size: 2.5×1.2×0.7 cm.
File:Gold-mz4b.jpg|Crystalline gold from Mina Zapata, [[Santa Elena de Uairen]], Venezuela. Size: 3.7×1.1×0.4 cm.
File:Gold-37466.jpg|Gold leaf from Harvard Mine, [[Jamestown, California]], USA. Size 9.3×3.2× >0.1 cm.
</gallery></center>

==Production==
{{Main|Gold prospecting|Gold mining|Gold extraction|List of countries by gold production}}
[[File:Gold (mined)2.png|thumb|300px|right|Global gold output in 2005.]]
[[File:Gold mine.jpg|thumb|250px|right|The entrance to an underground gold mine in [[Victoria, Australia|Victoria]], [[Australia]]]]
[[File:golddust.jpg|thumb|Pure gold precipitate produced by the [[aqua regia]] refining process]]
[[Gold extraction]] is most economical in large, easily mined deposits. Ore grades as little as 0.5&nbsp;mg/kg (0.5 parts per million, ppm) can be economical. Typical ore grades in [[open-pit mining|open-pit]] mines are 1–5&nbsp;mg/kg (1–5 ppm); ore grades in underground or [[Underground mining (hard rock)|hard rock]] mines are usually at least 3&nbsp;mg/kg (3 ppm). Because ore grades of 30&nbsp;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]]. Production in 1970 accounted for 79% of the world supply, producing about 1,480 [[tonne]]s. 2008 production was 2,260 tonnes. In 2007 [[China]] (with 276 tonnes) overtook South Africa as the world's largest gold producer, the first time since 1905 that South Africa has not been the largest.<ref>{{Cite web|last=Mandaro|first=Laura|url= http://www.marketwatch.com/news/story/china-now-worlds-largest-gold/story.aspx?guid=%7B8C528CE8%2D0262%2D485D%2DACEB%2D2247D18282CB%7D|title=China now world's largest gold producer; foreign miners at door – MarketWatch|publisher=MarketWatch|date=2008-01-17|accessdate=2009-04-05}}</ref>

The city of [[Johannesburg]] located in [[South Africa]] was founded as a result of the [[Witwatersrand Gold Rush]] which resulted in the discovery of some of the largest gold deposits the world has ever seen. Gold fields located within the basin in the [[Free State (South African province)|Free State]] and [[Gauteng]] provinces are extensive in [[strike and dip]] requiring some of the world's deepest mines, with the Savuka and [[TauTona]] mines being currently the world's deepest gold mine at 3,777 m. The [[Second Boer War]] of 1899–1901 between the [[British Empire]] and the [[Afrikaner]] [[Boer]]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]]. Mines in [[South Dakota]] and [[Nevada]] supply two-thirds of gold used in the United States. In South America, the controversial project [[Pascua Lama]] aims at exploitation of rich fields in the high mountains of [[Atacama Desert]], at the border between [[Chile]] and [[Argentina]]. Today about one-quarter of the world gold output is estimated to originate from artisanal or small scale mining.<ref>{{Cite journal|title= Removal of Barriers to the Abatement of Global Mercury Pollution from Artisanal Gold Mining|url=http://www.unido.org/fileadmin/import/10644_CHRISTIANtext.3.pdf|last=Beinhoff|first=Christian}}</ref>

After initial production, gold is often subsequently refined industrially by the [[Wohlwill process]] which is based on [[electrolysis]] or by the [[Miller process]], that is chlorination in the melt. The Wohlwill process results in higher purity, but is more complex and is only applied in small-scale installations.<ref>{{Cite book |url=http://books.google.com/?id=__lqGczo9TwC&pg=PA342|page=342 |title=Pollution prevention technology handbook |author=Noyes, Robert |publisher=William Andrew|year=1993 |isbn= 0815513119}}</ref><ref>{{Cite book |url=http://books.google.com/?id=E_u9ARrm37oC&pg=PA244 |page=244 |title=Industrial electrochemistry |author=Pletcher, Derek and Walsh, Frank |publisher=Springer |year=1990 |isbn=0412304104}}</ref> Other methods of assaying and purifying smaller amounts of gold include parting and inquartation as well as [[cupellation]], or refining methods based on the dissolution of gold in aqua regia.<ref>{{Cite book |url=http://books.google.com/?id=0NE1KjVISyAC&pg=PA210 |page=210|title=Separation, preconcentration, and spectrophotometry in inorganic analysis |author=Marczenko, Zygmunt and Balcerzak, María |publisher=Elsevier |year=2000 |isbn=0444505245}}</ref>

At the end of 2009, it was estimated that all the gold ever mined totaled 165,000 tonnes.<ref name="World Gold Council FAQ"/> 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.<ref>{{Cite news |date=13 April 2007 |title=Gold mine production costs up by 17% in 2006 while output fell |author=O'Connell, Rhona |url=http://www.mineweb.net/mineweb/view/mineweb/en/page33?oid=19485&sn=Detail}}</ref>

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.<ref>{{Cite web |url=http://www.lewrockwell.com/blumen/blumen14.html |title=The Myth of the Gold Supply Deficit |accessdate=2009-03-30}}</ref> 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.<ref>[http://www.gold-eagle.com/editorials_05/zurbuchen011506.html estimate of total gold loss over history] Accessed Nov. 10, 2010.</ref>

==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,<ref>{{Cite news|url= http://www.nakedcapitalism.com/2008/03/indias-love-affair-with-gold-tarnishing.html|title=India's love affair with gold tarnishing|date=March 27, 2008}}</ref> 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.<ref>{{Cite news|url=http://www.commodityonline.com/news/Gold-Why-China-outbeats-India-in-gold-reserves-17196-3-1.html|title=Gold: Why China outbeats India in gold reserves|date=2009-04-26|publisher=Commodity online}}</ref> Indian households hold 18,000 tonnes of gold which represents 11 per cent of the global stock and worth more than $950 billion.<ref>{{Cite news|url= http://economictimes.indiatimes.com/markets/commodities/indian-households-hold-over-950-billion-of-gold-macquarie/articleshow/10978409.cms|title=Indian households hold over $950 billion of gold: Macquarie|date=December 4, 2011}}</ref>

{| style="font-size: 95%; text-align: right;" class="wikitable sortable" border="0"
|+ Gold jewellery consumption by country (in Tonnes).<ref>{{Cite news|url=http://www.forexyard.com/en/news/Gold-jewellery-consumption-by-country-2011-02-28T130619Z-FACTBOX|title=Gold jewellery consumption by country|date=2009-02-28|publisher=FOREXYARD}}</ref>
|-
! '''Country''' !! '''2010''' !! '''2009''' !! '''% Change'''
|-
| align=left|{{flag|India}} || 745.70 || 442.37 || +69
|-
| align=left|[[Greater China]] || 428.00 || 376.96 || +14
|-
| align=left|{{flag|United States}} || 128.61 || 150.28 || -14
|-
| align=left|{{flag|Turkey}} || 74.07 || 75.16 || -1
|-
| align=left|{{flag|Saudi Arabia}} || 72.95 || 77.75 || -6
|-
| align=left|{{flag|Russia}} || 67.50 || 60.12 || +12
|-
| align=left|{{flag|United Arab Emirates}} || 63.37 || 67.60 || -6
|-
| align=left|{{flag|Egypt}} || 53.43 || 56.68 || -6
|-
| align=left|{{flag|Indonesia}} || 32.75 || 41.00 || -20
|-
| align=left|{{flag|United Kingdom}} || 27.35 || 31.75 || -14
|-
| align=left|Other Gulf Countries || 21.97 || 24.10 || -10
|-
| align=left|{{flag|Japan}} || 18.50 || 21.85 || -15
|-
| align=left|{{flag|South Korea}} || 15.87 || 18.83 || -16
|-
| align=left|{{flag|Vietnam}} || 14.36 || 15.08 || -5
|-
| align=left|{{flag|Thailand}} || 6.28 || 7.33 || -14
|-
| align=left|'''Total''' || '''1805.60''' || '''1508.70''' || '''+20'''
|-
| align=left|''Other Countries'' || ''254.0'' || ''251.6'' || ''+1''
|-
| align=left|'''World Total''' || '''2059.6''' || '''1760.3''' || '''+17'''
|}

==Pollution==
Gold production is also associated with contribution to hazardous pollution <ref>[http://www.scribd.com/doc/82418790/Gold-groduction-and-its-environmental-impact  Summit declaration of Peoples‘ Gold summit, San Juan Ridge, California in June 1999”] </ref>. The ore generally containing less than one ppm gold metal, is ground and mixed with [[Sodium cyanide]] or Mercury to react with gold in the ore for gold separation. Cyanide is highly poisonous chemical, which can kill living creatures when exposed in minute quantities. Many cyanide spills<ref> [http://www.deseretnews.com/article/810435/Cyanide-spill-compared-to-Chernobyls---N-disaster.html  Cyanide spills from gold mine compared to Chernobyls nuclear disaster] </ref> from gold mines have taken place worldwide both in developed and poor countries which killed the marine life in long stretch of effected rivers. Environmentalists consider these pollution disasters as major environmental disasters<ref> [http://news.bbc.co.uk/2/hi/europe/642880.stm  Death of a river]</ref> <ref> [http://www.abc.net.au/am/stories/s98890.htm  Cyanide spill second only to Chernobyl] </ref>. When mercury is used in gold production, minute quantity of mercury compounds enter in to water bodies causing heavy metal contamination of water. Mercury enters in to human food chain in the form of [[Methyl mercury]] through fish, etc. Mercury poisoning in humans causes incurable severe retardation of brain functions.
Thirty tons of used ore is dumped as waste for producing one finger ring of gold <ref>[http://www.latrobefinancialmanagement.com/Research/Commodities/Behind%20Gold's%20Glitter%20NYTimes%20Piece.pdf  Behind gold’s glitter, torn lands and pointed questions, New York times, October 24, 2005]</ref>. Gold ore dumps are the source of many heavy metals such as cadmium, lead, zinc, copper, [[Arsenic]], [[Selenium]] and mercury. Water is unsuitable for human consumption if these [[Heavy metal (chemistry)]] are found in more than one ppm concentration. When sulphide bearing minerals in these ore dumps are exposed to air and water, the sulphide transforms in to sulphuric acid which in turn dissolves the heavy metals facilitating their passage in to surface water and ground water. This process is called [[Acid mine drainage]]. The gold ore dumps are considered as long term man made hazardous waste next only to nuclear waste dumps <ref>[http://www.latrobefinancialmanagement.com/Research/Commodities/Behind%20Gold's%20Glitter%20NYTimes%20Piece.pdf  Behind gold’s glitter, torn lands and pointed questions, New York times, October 24, 2005]</ref>. Billions of dollars need to be spent to mitigate the heavy metals pollution from worldwide gold ore dumps which are increasing every year.
Gold extraction is also highly energy intensive industry (25 kwh of electricity per one gram of gold production) to extract ore from deep mines and to grind the large quantity of ore for further chemical extraction<ref>[http://www.sciencedirect.com/science/article/pii/S0959652612000947 Using life cycle assessment to evaluate some environmental impacts of gold]</ref>. 

==Chemistry==
[[File:Gold(III) chloride solution.jpg|thumb|right|Gold (III) chloride solution in water]]

Although gold is a [[noble metals|noble metal]], it forms many and diverse compounds. The [[oxidation state]] of gold in its compounds ranges from −1 to +5, but Au(I) and Au(III) dominate its chemistry. Au(I), referred to as the aurous ion, is the most common oxidation state with soft [[ligand]]s such as [[thioether]]s, [[thiolate]]s, and tertiary [[phosphine]]s. Au(I) compounds are typically linear. A good example is [[gold cyanidation|Au(CN)<sub>2</sub><sup>−</sup>]], which is the soluble form of gold encountered in mining. Curiously, aurous complexes of water are rare. The binary [[gold halide]]s, such as [[gold(I) chloride|AuCl]], form zigzag polymeric chains, again featuring linear coordination at Au. Most drugs based on gold are Au(I) derivatives.<ref>{{Cite journal|author=Shaw III, C. F.|title=Gold-Based Medicinal Agents|journal=Chemical Reviews|year=1999|volume=99|issue=9|pages= 2589–2600|doi=10.1021/cr980431o|pmid=11749494}}</ref>

Au(III) (auric) is a common oxidation state, and is illustrated by [[gold(III) chloride]], Au<sub>2</sub>Cl<sub>6</sub>. The gold atom centers in Au(III) complexes, like other d<sup>8</sup> compounds, are typically [[square planar]], with [[chemical bond]]s that have both [[covalent]] and [[ion]]ic character.

[[Aqua regia]], a 1:3 mixture of [[nitric acid]] and [[hydrochloric 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 AuCl<sub>4</sub><sup>−</sup> ions, or [[chloroauric acid]], thereby enabling further oxidation.

Some free [[halogen]]s react with gold.<ref>{{Cite book|author=Wiberg, Egon; Wiberg, Nils and Holleman, Arnold Frederick |year=2001|title=Inorganic Chemistry|edition= 101|publisher=Academic Press|isbn=0123526515|pages=1286}}</ref><!-- although it is more than a little silly to ask for a citation for this given that anyone who has taken high school chemistry can tell you free halogens will react with basically anything --> Gold also reacts in alkaline solutions of [[potassium cyanide]]. With mercury, it forms an [[amalgam (chemistry)|amalgam]].

===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<sup>−</sup> [[anion]], called aurides. [[Caesium auride]] (CsAu), for example, crystallizes in the [[caesium chloride]] motif.<ref name="relativist_Au_Pt">{{Cite journal|title=Effects of relativistic motion of electrons on the chemistry of gold and platinum|first=Martin|last=Jansen|journal=Solid State Sciences|volume=7|issue= 12|year = 2005|doi=10.1016/j.solidstatesciences.2005.06.015|pages=1464–1474|bibcode=2005SSSci...7.1464J}}</ref> Other aurides include those of [[rubidium|Rb]]<sup>+</sup>, [[potassium|K]]<sup>+</sup>, and tetramethylammonium (CH<sub>3</sub>)<sub>4</sub>N<sup>+</sup>.<ref name=Holleman>Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.</ref> Gold has the highest [[electronegativity|Pauling electronegativity]] 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(CH<sub>2</sub>)<sub>2</sub>P(C<sub>6</sub>H<sub>5</sub>)<sub>2</sub>]<sub>2</sub>Cl<sub>2</sub>. The evaporation of a solution of {{chem|Au(OH)|3}} in concentrated {{chem|H|2|SO|4}} produces red crystals of gold(II) sulfate, Au<sub>2</sub>(SO<sub>4</sub>)<sub>2</sub>. Originally thought to be a mixed-valence compound, it has been shown to contain {{chem|Au|2|4+}} cations.<ref>{{Cite journal|doi= 10.1002/1521-3749(200109)627:9<2112::AID-ZAAC2112>3.0.CO;2-2|author=Wickleder, Mathias S.|year=2001|title=AuSO4: A True Gold(II) Sulfate with an Au4+2 Ion|journal=Journal of Inorganic and General Chemistry|volume=627|pages=2112–2114|issue= 9}}</ref><ref>{{Cite book| title = Handbook of chalcogen chemistry: new perspectives in sulfur, selenium and tellurium|author=Wickleder, Mathias S.|editor= Francesco A. Devillanova|publisher=Royal Society of Chemistry|year=2007|isbn=0854043667|pages=359–361|url=http://books.google.com/?id=IvGnUAaSqOsC&pg=PA359}}</ref> A noteworthy, legitimate gold(II) complex is the [[tetraxenonogold(II)]] cation, which contains [[xenon]] as a ligand, found in [AuXe<sub>4</sub>](Sb<sub>2</sub>F<sub>11</sub>)<sub>2</sub>.<ref>{{Cite journal|author=Seidel, S.; Seppelt, K.|title=Xenon as a Complex Ligand: The Tetra Xenono Gold(II) Cation in AuXe<sub>4</sub><sup>2+</sup>(Sb<sub>2</sub>F<sub>11</sub><sup>−</sup>)<sub>2</sub>|journal=Science|year=2000|volume=290|issue=5489|pages=117–118|doi= 10.1126/science.290.5489.117|pmid=11021792|bibcode = 2000Sci...290..117S }}</ref>

[[Gold pentafluoride]], along with its derivative anion, {{chem|AuF|6|-}}, and its [[difluorine complex]], [[gold heptafluoride]], is the sole example of gold(V), the highest verified oxidation state.<ref>{{Cite journal|author=Riedel, S.; Kaupp, M.|title=Revising the Highest Oxidation States of the 5d Elements: The Case of Iridium(+VII)|journal=Angewandte Chemie International Edition|year=2006|volume=45|issue=22|pmid=16639770|pages=3708–3711|doi= 10.1002/anie.200600274}}</ref>

Some gold compounds exhibit ''[[aurophilicity|aurophilic bonding]]'', which describes the tendency of gold ions to interact at distances that are too long to be a conventional Au–Au bond but shorter than [[Van der Waals force|van der Waals bonding]]. The interaction is estimated to be comparable in strength to that of a [[hydrogen bond]].

===Mixed valence compounds===
Well-defined cluster compounds are numerous.<ref name=Holleman/> In such cases, gold has a fractional oxidation state. A representative example is the octahedral species {Au([[Triphenylphosphine|P(C<sub>6</sub>H<sub>5</sub>)<sub>3</sub>]])}<sub>6</sub><sup>2+</sup>. [[Gold chalcogenides]], 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<ref>{{Cite web|title=Gold MSDS|url=http://www.espi-metals.com/msds's/gold.htm|publisher=Electronic Space Products International|author=Dierks, S|month=May|year=2005}}</ref> and is sometimes used as a food decoration in the form of [[gold leaf]]. Metallic gold is also a component of the alcoholic drinks [[Goldschläger]], [[Gold Strike (drink)|Gold Strike]], and [[Goldwasser]]. Metallic gold is approved as a [[food additive]] in the EU ([[E number|E175]] in the [[Codex Alimentarius]]). 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]]) such as [[gold(I,III) chloride|gold chloride]] are toxic to the liver and kidneys. Common cyanide salts of gold such as potassium gold cyanide, used in gold electroplating, are toxic by virtue of both their cyanide and gold content. There are rare cases of lethal gold poisoning from [[potassium gold cyanide]].<ref>{{Cite journal|author =Wright, I. H.; Vesey, C. J.|year = 1986|title = Acute poisoning with gold cyanide|journal=Anaesthesia|volume =41|issue = 79|pages = 936–939|doi = 10.1111/j.1365-2044.1986.tb12920.x|pmid=3022615}}</ref><ref>{{Cite journal|author = Wu, Ming-Ling; Tsai, Wei-Jen; Ger, Jiin; Deng, Jou-Fang; Tsay, Shyh-Haw; Yang, Mo-Hsiung.|journal = Clinical toxicology|year = 2001|volume = 39|issue = 7|pages = 739–743|title = Cholestatic Hepatitis Caused by Acute Gold Potassium Cyanide Poisoning|doi = 10.1081/CLT-100108516|pmid = 11778673}}</ref> Gold toxicity can be ameliorated with [[chelation therapy]] with an agent such as [[Dimercaprol]].

Gold metal was voted [[Allergen of the Year]] in 2001 by the American Contact Dermatitis Society. Gold contact allergies affect mostly women.<ref>[http://www.entrepreneur.com/tradejournals/article/149265914.html Henna tattoo ingredient is Allergen of the Year.(Clinical Rounds)]. Retrieved Sept 17, 2009.</ref> Despite this, gold is a relatively non-potent contact allergen, in comparison with metals like [[nickel]].<ref>{{Cite news|url=http://www.highbeam.com/doc/1G1-176478357.html|title=Ubiquitous nickel wins skin contact allergy award for 2008|date=February 15, 2008|author=Brunk, Doug}}</ref>

==Price==
[[File:Gold price in USD.png|thumb|300px|Gold price history in 1960-2011]]
Like other precious metals, gold is measured by [[troy weight]] and by grams. When it is alloyed with other metals the term ''[[carat (purity)|carat]]'' 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]] or coin can also be expressed as a decimal figure ranging from 0 to 1, known as the [[millesimal fineness]], such as 0.995 being very pure.

The price of gold is determined through trading in the gold and [[derivative (finance)|derivatives]] markets, but a procedure known as the [[Gold Fixing]] in [[London]], originating in September 1919, provides a daily benchmark price to the industry. The afternoon fixing was introduced in 1968 to provide a price when US markets are open.

Historically gold [[Mint (coin)|coinage]] was widely used as currency; when [[paper money]] was introduced, it typically was a [[receipt]] redeemable for gold coin or bullion. In a [[monetary]] system known as the [[gold standard]], a certain [[weight]] of gold was given the name of a unit of currency. For a long period, the United States government set the value of the US dollar so that one [[troy ounce]] was equal to $20.67 ($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 [[devaluation|currency devaluation]] against increased gold demand.

[[File:Goldkey logo removed.jpg|thumb|right|A Swiss-cast 1 kg [[gold bar]].]]
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]]s still hold historical [[official gold reserves|gold reserves]] as a [[store of value]] although the level has generally been declining. The largest gold depository in the world is that of the [[Federal Reserve System|U.S. Federal Reserve Bank]] in [[New York]], which holds about 3%<ref name='ISAMPE 2006-11-22'>{{cite web | url = http://sinai.apphy.u-fukui.ac.jp/gcj/publications/gold/gold.pdf | title = THE HIDDEN BEAUTY OF GOLD | accessdate = 2011-05-10 | last = Hitzer | first = Eckhard | coauthors = Perwass, Christian | date = 2006-11-22 }}</ref> of the gold ever mined, as does the similarly laden [[United States Bullion Depository|U.S. Bullion Depository]] at [[Fort Knox]].
In 2005 the [[World Gold Council]] estimated total global gold supply to be 3,859 tonnes and demand to be 3,754 tonnes, giving a surplus of 105 tonnes.<ref>{{Cite web|url=http://www.gold.org/value/stats/statistics/gold_demand/index.html|title=World Gold Council > value > research & statistics > statistics > supply and demand statistics|accessdate=2006-07-22}}</ref>

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).<ref>[http://kitco.com/LFgif/au75-pres.gif Kitco.com], Gold – London PM Fix 1975 – present (GIF), Retrieved 2006-07-22.</ref> The period from 1999 to 2001 marked the "[[Brown Bottom]]" after a 20-year [[bear market]].<ref>[http://www.timesonline.co.uk/tol/news/politics/article1655001.ece "Goldfinger Brown's £2 billion blunder in the bullion market"]. ''[[The Times]]'' (London), 15 April 2007.</ref> 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 weight|troy ounce]] was set.<ref name="LBMA statistics">{{Cite web|url=http://www.lbma.org.uk/2008dailygold.htm |title=LBMA statistics |publisher=Lbma.org.uk |date=2008-12-31 |accessdate=2009-04-05}}</ref> Another record price was set on March 17, 2008 at $1023.50/oz ($32,900/kg).<ref name="LBMA statistics"/> 

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.<ref>{{Cite news|url=http://news.bbc.co.uk/2/hi/business/8390779.stm |title=Gold hits yet another record high |publisher=[[BBC News]] |date=2009-12-02 |accessdate=2009-12-06}}</ref> Gold further rallied hitting new highs in May 2010 after the European Union debt crisis prompted further purchase of gold as a safe asset.<ref>{{Cite news|title=PRECIOUS METALS: Comex Gold Hits All-Time High |newspaper=[[The Wall Street Journal]] |date=May 11, 2010 |url=http://online.wsj.com/article/BT-CO-20100511-717954.html |accessdate=August 4, 2010}} {{Dead link|date=September 2010|bot=H3llBot}}</ref><ref>{{Cite web|url=http://www.marketwatch.com/story/gold-prices-resume-rise-as-eu-plan-pondered-2010-05-11 |title=Gold futures hit closing record as investors fret rescue deal |last1= Gibson |first1=Kate |last2= Chang |first2= Sue |date=May 11, 2010 |publisher=[[MarketWatch]] |accessdate=August 4, 2010}}</ref> On March 1, 2011, gold hit a new all-time high of $1432.57, based on [[Gold as an investment|investor]] concerns regarding ongoing [[2010–2011 Middle East and North Africa protests|unrest]] in [[North Africa]] as well as in the [[Middle East]].<ref>{{Cite web|url=http://uk.news.yahoo.com/22/20110301/tbs-uk-markets-global-4210405.html|title=Gold hits record, oil jumps with Libya unrest |publisher=[[yahoo.com]] |date=March 1, 2011 |accessdate=March 1, 2011}}</ref>

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,<ref>{{Cite web|url=http://www.bloomberg.com/news/2011-08-25/cash-gold-may-advance-after-dropping-most-in-18-months-as-shares-rebound.html|title=Gold Extends Biggest Decline in 18 Months After CME Raises Futures Margins|publisher=www.bloomberg.com|date=August 23, 2011 |accessdate=August 30, 2011}}</ref> prompting speculation that this long [[secular bear market]] has ended and a [[bull market]] has returned.<ref>{{Cite web|url=http://www.ameinfo.com/75511.html |title=Gold starts 2006 well, but this is not a 25-year high!&#124;Financial Planning |publisher=Ameinfo.com|accessdate=2009-04-05}}</ref>

==Symbolism==
[[File:GoldBarAtGrandEmperorCasino.JPG|thumb|Gold bars at the Emperor Casino in [[Macau]]]]
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]]s, golden [[trophy|trophies]] and other decorations. Winners of athletic events and other graded competitions are usually awarded a gold medal (e.g., the [[Olympic Games]]). Many awards such as the [[Nobel Prize]] are made from gold as well. Other award statues and prizes are depicted in gold or are [[gold plated]] (such as the [[Academy Awards]], the [[Golden Globe Awards]], the [[Emmy Awards]], the [[Palme d'Or]], and the [[British Academy Film Awards]]).

[[Aristotle]] in his [[Aristotelian ethics|ethics]] used gold symbolism when referring to what is now commonly known as the [[golden mean (philosophy)|golden mean]]. Similarly, gold is associated with perfect or divine principles, such as in the case of the [[golden ratio]] and the [[golden rule]].

Gold is further associated with the wisdom of aging and fruition. The fiftieth [[wedding anniversary]] is golden. Our precious latter years are sometimes considered "golden years". The height of a civilization is referred to as a "[[golden age]]".

In [[Christianity]] gold has sometimes been associated with the extremities of utmost evil and the greatest sanctity. In the [[Book of Exodus]], the [[Golden Calf]] is a symbol of [[idolatry]]. In the [[Book of Genesis]], [[Abraham]] was said to be rich in gold and [[silver]], and Moses was instructed to cover the [[Mercy Seat]] of [[Ark of the Covenant|the Ark of the Covenant]] with pure gold. In Christian art the [[Halo (religious iconography)|halos]] of [[Christ]], [[Virgin Mary|Mary]] and the Christian [[saints]] are golden.

Medieval kings were inaugurated under the signs of [[anointing|sacred oil]] and a golden crown, the latter symbolizing the eternal shining light of heaven and thus a Christian king's divinely inspired authority. [[Wedding ring]]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 [[Eastern Orthodox Church|Orthodox Christianity]], 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]] Legislature designated gold "the State Mineral and mineralogical emblem."<ref>[http://www.leginfo.ca.gov/cgi-bin/displaycode?section=gov&group=00001-01000&file=420-429.8 California Government Code selection 420–429.8] (see § 425.1)</ref>

In 1968, the [[Alaska]] Legislature named gold "the official state mineral."<ref>[http://www.legis.state.ak.us/cgi-bin/folioisa.dll/stattx08/query=*/doc/%7B@17998%7D? Alaska Statutes] (see§ 44.09.110)</ref>

==See also==
{{colbegin|3}}
*[[Bulk leach extractable gold]]
*[[Commodity fetishism]] (Marxist economic theory)
*[[Digital gold currency]]
*[[Gold Anti-Trust Action Committee]]
*[[Gold fingerprinting]]
*[[Gold phosphine complex]]
*[[Gold Prospectors Association of America]]
*[[Mining in Roman Britain]]
*[[Prospecting]]
*[[Tumbaga]]
*[[Drinking water quality standards]]
{{colend}}

==References==
{{Reflist|colwidth=30em}}

==External links==
{{wikiquote}}
{{Commons}}
{{Wiktionary}}
*[http://www.lateralscience.co.uk/gold/auriferous.html ''Getting Gold'' 1898 book], www.lateralscience.co.uk
*[http://www.epa.gov/epaoswer/other/mining/techdocs/gold.pdf Technical Document on Extraction and Mining of Gold], www.epa.gov
*[http://www.pniok.de/au.htm Picture in the Element collection from Heinrich Pniok], www.pniok.de
*[http://www.rsc.org/chemistryworld/podcast/element.asp Chemistry in its element podcast] (MP3) from the [[Royal Society of Chemistry]]'s [[Chemistry World]]: [http://www.rsc.org/images/CIIE_Gold_48k_tcm18-118269.mp3 Gold] www.rsc.org

{{Jewellery}}
{{Compact periodic table}}
{{Gold compounds}}

[[Category:Gold| ]]
[[Category:Chemical elements]]
[[Category:Dental materials]]
[[Category:Electrical conductors]]
[[Category:Noble metals]]
[[Category:Precious metals]]
[[Category:Transition metals]]
[[Category:Cubic minerals]]
[[Category:Warrants issued in Hong Kong Stock Exchange]]
<!-- [[Category:Gold bubbles]] -->

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[[za:Gim]]
[[vec:Oro]]
[[vep:Kuld]]
[[vi:Vàng]]
[[fiu-vro:Kuld]]
[[wa:Ôr]]
[[zh-classical:金]]
[[war:Bulawan]]
[[wuu:金]]
[[yi:גאלד]]
[[yo:Wúrà]]
[[zh-yue:金]]
[[diq:Zern]]
[[bat-smg:Auksos]]
[[zh:金]]