Gold is a chemical element with symbol Au (from Latin: aurum) and atomic number
79. In its purest form, it is a bright, slightly reddish yellow, dense, soft, ma
lleable and ductile metal. Chemically, gold is a transition metal and a group 11
element. It is one of the least reactive chemical elements, and is solid under
standard conditions. The metal therefore occurs often in free elemental (native)
form, as nuggets or grains, in rocks, in veins and in alluvial deposits. It occ
urs in a solid solution series with the native element silver (as electrum) and
also naturally alloyed with copper and palladium. Less commonly, it occurs in mi
nerals as gold compounds, often with tellurium (gold tellurides).
Gold's atomic number of 79 makes it one of the higher atomic number elements tha
t occur naturally in the universe. It is thought to have been produced in supern
ova nucleosynthesis and to have been present in the dust from which the Solar Sy
stem formed. Because the Earth was molten when it was just formed, almost all of
the gold present in the early Earth probably sank into the planetary core. Ther
efore most of the gold that is present today in the Earth's crust and mantle is
thought to have been delivered to Earth later, by asteroid impacts during the la
te heavy bombardment, about 4 billion years ago.
Gold resists attacks by individual acids, but it can be dissolved by aqua regia
("royal water" [nitro-hydrochloric acid], so named because it dissolves "the kin
g of metals"). The acid mixture causes the formation of a soluble gold tetrachlo
ride anion. Gold metal also dissolves in alkaline solutions of cyanide, which ar
e used in mining and electroplating. It dissolves in mercury, forming amalgam al
loys; it is insoluble in nitric acid, which dissolves silver and base metals, a
property that has long been used to confirm the presence of gold in items, givin
g rise to the term acid test.
This metal has been a valuable and highly sought-after precious metal for coinag
e, jewelry, and other arts since long before the beginning of recorded history.
In the past, a gold standard was often implemented as a monetary policy within a
nd between nations, but gold coins ceased to be minted as a circulating currency
in the 1930s, and the world gold standard (see article for details) was finally
abandoned for a fiat currency system after 1976. The historical value of gold w
as rooted in its medium rarity, easy handling and minting, easy smelting, non-co
rrodability, distinct color, and non-reactivity to other elements.
A total of 174,100 tonnes of gold have been mined in human history, according to
GFMS as of 2012. This is roughly equivalent to 5.6 billion troy ounces or, i
n terms of volume, about 9020 m3, or a cube 21 m on a side. The world consumptio
n of new gold produced is about 50% in jewelry, 40% in investments, and 10% in i
Gold s high malleability, ductility, resistance to corrosion and most other chemic
al reactions, and conductivity of electricity have led to its continued use in c
orrosion resistant electrical connectors in all types of computerized devices (i
ts chief industrial use). Gold is also used in infrared shielding, colored-glass
production, and gold leafing. Certain gold salts are still used as anti-inflamm
atories in medicine.