Editing Period 6 element (section)

===Gold===
{{main|Gold}}
'''Gold''' is a dense, soft, shiny, malleable and ductile metal.  It is a [[chemical element]] with the symbol '''Au''' and [[atomic number]] 79.

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 chemical elements solid under standard conditions. 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 a common basis for [[monetary policy|monetary policies]] throughout human history,{{Citation needed|date=April 2012}} later being supplanted by [[fiat currency]] starting in the 1930s. The last [[gold certificate]] and [[gold coin]] currencies were issued in the U.S. in 1932. In Europe, most countries left the gold standard with the start of [[World War I]] in 1914 and, with huge war debts, failed to return to gold as a medium of exchange.

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]. www.gold.org</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.|access-date = 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.

It has been claimed that most of the Earth's gold lies at its core, the metal's high density having made it sink there in the planet's youth.  Virtually all of the gold that mankind has discovered is considered to have been deposited later by [[meteorites]] which contained the element.  This supposedly explains why, in prehistory, gold appeared as nuggets on the earth's surface.<ref>{{cite news| url=https://www.bbc.co.uk/news/science-environment-14827624 | work=BBC News | title=Meteorites delivered gold to Earth | date=2011-09-08}}</ref><ref>{{Cite web | url=https://www.sciencedaily.com/releases/2011/09/110907132044.htm |title = Where does all Earth's gold come from? Precious metals the result of meteorite bombardment, rock analysis finds}}</ref><ref>{{Cite journal |last1=Kirk |first1=Jason |last2=Ruiz |first2=Joaquin |last3=Chesley |first3=John |last4=Titley |first4=Spencer |date=2003 |title=The Origin of Gold in South Africa |url=http://www.sas.rochester.edu/ees/ees119/reading2.pdf |journal=American Scientist |volume=91 |issue=6 |pages=534–541 |doi=10.1511/2003.38.534 |issn=0003-0996}}</ref><ref>{{cite news| url=http://www.huffingtonpost.com/2011/09/10/meteor-shower-gold_n_955448.html | work=Huffington Post | title=Meteor Shower Rained Gold On Ancient Earth | date=2011-09-10}}</ref><ref>{{Cite journal |doi = 10.1038/nature10399|pmid = 21901010|title = The tungsten isotopic composition of the Earth's mantle before the terminal bombardment|journal = Nature|volume = 477|issue = 7363|pages = 195–198|year = 2011|last1 = Willbold|first1 = Matthias|last2 = Elliott|first2 = Tim|last3 = Moorbath|first3 = Stephen|bibcode = 2011Natur.477..195W|s2cid = 4419046}}</ref>