CALAVERITE MINERAL FACTS Nevada Turquoise gem stones
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Calaverite Mineral Facts:

Chemical Formula: AuTe2 (Usually contains a little silver)  44% Gold by weight

Colors: Silver-white or bronzy yellow in color and has a yellow-gray or greenish gray streak. Its surface is frequently covered with a yellow tarnish.

Hardness: 2 to 3
Hardness varies somewhat depending on formation and impurities.

Density: 9.4
The density is high because of the large gold content. 

Cleavage: The mineral is brittle and without distinct cleavage.

Crystallography: Monoclinic
Calaverite crystallizes in the monoclinic system in crystals that are elongated parallel to the orthoaxis and deeply striated in this direction.  Twinning is common and the resulting twins are very complicated. Usually, however, the mineral occurs massive and granular.

Luster:. Metallic luster.

Optics: (Refractive Index):  Opaque


Composition, Structure and Associated Minerals:
Calaverite is a nearly pure gold telluride. However, it is usually intermixed with small quantities of the silver telluride. Calaverite is chiefly important as an ore of gold. While occurring only in a few places, they are sufficiently abundant at some of them to be the main ore mined at these locations.

Identification and Diagnostics
On charcoal before the blowpipe the mineral fuses easily to a yellow globule of gold, yielding at the same time the fumes of tellurium oxide. It dissolves in concentrated H2SO4, producing a deep red solution (a positive test for telluride ion). When treated with HNO3 it decomposes, leaving a rusty mass of spongy gold. The solution treated with HC1 usually yields a slight precipitate of silver chloride. Distinguished from sylvanite by the small amount of silver present and by its lack of a cleavage.  It is distinguished from krennerite by its mode of crystallization.

Occurrence, Localities and Origins:
The mineral occurs in veins with the other tellurides associated with gold ores in Calaveras Co., California in the Stanislaus Mine,  where it was first recognized.  Calaverite and other associated gold and silver telluride minerals are important sources of silver and gold in the mines at Nagyag, Transylvania, at Cripple Creek and in Boulder Co., Colo., and at Kalgoorlie, W. Australia.

It is believed to have been deposited by ascending magmatic water at comparatively low temperatures. Other rare tellurides belonging to this group are,  sylvanite, hessite (Ag2Te) and petzite (Au,Ag2Te), krennerite, AuTe2 , and nagyagite, a sulpho-telluride of lead and gold. Historically, calaverite has been as important ore of gold.

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Calaverite, Needle Crystals



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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