It is unaffected by moisture, oxygen, or ordinary acids but is attacked by the halogens . A relatively soft metal, gold is usually hardened by alloying with copper, silver, or other metals. White gold, a substitute for platinum, is an alloy of gold with platinum, palladium, nickel, or nickel and zinc. Green gold, also used by jewelers, is usually an alloy of gold with silver. Alloys of gold with copper are a reddish yellow and are used for coinage and jewelry.
Most gold is found in the metallic state in the form of dust, grains, flakes, or nuggets.
It occurs, usually in association with silver or other metals, in quartz veins or lodes so finely disseminated that it is not visible. It is found also in alluvial placer deposits, which are worked by panning, dredging, and hydraulic mining. It also occurs in compounds, notably telluride minerals. Gold has been known from prehistoric times and was possibly the first metal used by humans. In the Middle Ages alchemists sought to transmute baser metals into gold.