Gold

native element

pyrite

Formula: Au native element
Specific gravity: 15.5 - 19.3
Hardness: 2½ to 3
Streak: Shining yellow
Colour: Shining yellow
Solubility: Insoluble in hydrochloric, sulphuric and nitric acids
Melting Point: 1062.4° ± 0.8°
Environments:

Plutonic igneous environments
Carbonatites
Placer deposits (typical)
Hydrothermal environments (typical)

Gold is a rare element that is widely distributed but in small amounts. Most gold occurs as the native metal. The chief sources of gold are hypothermal (high temperature), mesothermal (moderate temperature) and epithermal (low temperature) hydrothermal gold-quartz veins, together with pyrite and other sulphides. When gold-bearing veins are weathered, the gold liberated either remains in place in the soil mantle, or is washed into neighbouring streams to form placer deposits. Gold is usually primary, but it can also occur as a secondary mineral derived from gold tellurides.

At the Griffins Find gold deposit, about 15 km northwest of Lake Grace, Western Australia, gold occurred in quartz-sulphide lodes in metamorphosed greenstone which had been intruded by granitic rocks. The gold was closely associated with löllingite and arsenopyrite (AJM 20.1.7).

Pseudomorphs of gold after pyrite are extremely rare, but examples so well formed that they seem artificial are found at the Lena goldfields, Bodaibo Area, Eastern Siberia, Russia (R&M 92.5.410-423).

At the Colorado quartz gold mine, Mariposa county, California, USA, spectacular gold specimens have been found on a quartz matrix (R&M 94.4.370-372).

Common impurities: Ag,Cu,Pd,Hg

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