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Gold Mineral Facts:

Chemical Formula: Au 

Colors: The mineral is various shades of metallic yellow, depending upon purity, becoming paler with increase in the percentage of silver present.

Hardness: 2.5 to 3
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Density: 15.6 to 19.3
Density varies somewhat depending on impurities - the purer the heavier.

Cleavage: None  

Crystallography: Isometric
Sometimes found as octahedral crystals. Usually in irregular plates, scales or masses, seldom definitely crystallized. Gold is also found arborescent crystal groups with crystals elongated in the direction of an octahedral axis. Crystals are irregularly distorted to the point of passing into filiform, reticulated and dendritic shapes.

Luster:. Metallic, with a yellow streak.

Optics: (Refractive Index):  Opaque

Octahedral Gold crystals attached together, specimen from California

Composition, Structure and Associated Minerals:
Gold is soft, malleable and ductile. Its luster is, of course, metallic and its streak, yellow. When pure its density is 19.3, and its melting point 1063. It is not acted upon by water or the atmosphere, and it is a good conductor of electricity. Native gold is found in the quartz of veins cutting through granite and schistose rocks, commonly associated with sulfides such as pyrite, chalcopyrite, sphalerite, galena, stibnite, cinnabar and arsenopyrite. Non metallic gangue minerals include limonite and calcite. As a placer it is found in the gravels and sands of rivers whose channels cut through regions of quartz of veins, and in the sands of beaches bordering gold-producing districts. In placers it is associated with heavy minerals which accumulate with it.

Identification and Diagnostics
Easily fusible at 2.5-3. It is insoluble in ordinary acids but but it is readily dissolved in a mixture of nitric and hydrochloric acids (aqua regia). Gold is distinguished from certain yellow sulfides (particularly pyrite and chalcopyrite) and from yellow flakes of altered micas by its malleability, its insolubility and its great density.

Occurrence, Localities and Origins:
Although gold is a rare element, it is found widely distributed in nature, occurring in small amounts. The gold in quartz veins occurs as grains and scales scattered through quartz irregularly, often in such small particles as to be invisible to the naked eye, or as aggregates of crystals in cavities in the quartz. Pyrite is nearly always associated with the gold. On surfaces exposed to the weather the pyrite rusts out and stains the quartz, leaving it cavernous or cellular. It is also present in trace quantities in many rocks, especially acidic igneous rocks, and is disseminated through pyrite (FeS2) and some other sulfur compounds and their oxidation products. Gold, on account of its great weight and resistance to corrosion, is mechanically sorted in running water from the lighter material of the sands and gravels in which it may occur. Much of the world's historic supply of gold has come from placers. These are accumulations of sand or gravel in the beds of old river courses. The sands of modern streams often contain considerable quantities of gold.

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To view additional Gold Photos see:

Gold Nugget Photos
and
Even More Gold Nugget Photos

The famous Golden Bear Nugget From California

Nevada Outback Gems