GOLD MINERAL FACTS Nevada Turquoise gem stones
The Gem and Mineral Collector's Photo Gallery by Nevada Outback


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
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.

Important gold-producing countries include: South Africa, Australia, the USA, Russia, Mexico and Canada, and ore recently, China. Gold has been obtained in large quantity along the eastern flanks of the Ural Mountains, this having been the most productive region in the world between the years 1819 and 1849. In Russia gold has been mined in western Siberia and the Urals, in the Irkutsk Province, in Transbaikalia and Amur. Important production has also come from the mountains of southeastern Brazil, and from the highlands of many of the Central and South American countries. The western portion of the United States, more particularly from the western slopes of the Sierra Nevada Mountains, the state of Nevada and the higher portions of the Rocky Mountains. Gold bearing quartz veins have been worked at various points in Alaska, at Porcupine, Ontario, and other points in Canada. The region of South Africa known as the Rand, near Johannesburg in the Transvaal, has historically been the most productive gold district in the world. The gold occurs here scattered throughout inclined beds or "reefs" of a quartzose conglomerate, which has been mined to great depths. Australia has the following chief gold districts: Kalgoorlie in western Australia (largely tellurides), Ballarat and Bendigo in Victoria, Mount Morgan in Queensland and various fields in New South Wales. The production of Mexico comes chiefly from the districts of Guanajuato, El Oro and Dolores. The bulk of the production from Nevada comes from sedimentary hosted "Carlin Type deposits".

The great placer mines of the world are in California, Australia and Alaska. In Australia the principal gold mines are situated in the streams rising in the mountains of New South Wales and their extension into Victoria. A century ago, the valleys of the Yukon and other rivers in Alaska attracted much attention, as did the beach sands off Nome, which have yielded much of the metal.

Return to the Mineral Collectors Information Page

To view additional Gold Photos see:

Gold Nugget Photos
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Mojave Nugget from Randsburg, stringer area



Please note that the author, Chris Ralph, retains all copyrights to this entire document and it may not be reproduced, quoted or copied without permission.

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