Sylvanite

Sylvanite
Sylvanite from the Cripple Creek mining district
General
Category	Telluride mineral
Formula (repeating unit)	(Ag,Au)Te2
Strunz classification	2.EA.05
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P2/c
Identification
Formula mass	429.89 g/mol
Color	Silver-grey, Silver-white
Crystal habit	Massive to Crystalline
Cleavage	Perfect on the {010}
Fracture	Uneven
Tenacity	Brittle
Mohs scale hardness	1.5-2
Luster	Metallic
Streak	steel grey
Diaphaneity	opaque
Specific gravity	8.2
Density	8.1
Optical properties	Anisotropic
Pleochroism	None
Ultraviolet fluorescence	None
References

Sylvanite or silver gold telluride, (Ag,Au)Te₂, is the most common telluride of gold.

The gold:silver ratio varies from 3:1 to 1:1. It is a metallic mineral with a color that ranges from a steely gray to almost white. It is closely related to calaverite, which is more purely gold telluride with 3% silver. Sylvanite crystallizes in the monoclinic 2/m system. Crystals are rare and it is usually bladed or granular. It is very soft with a hardness of 1.5 - 2. It has a high relative density of 8 - 8.2. Sylvanite is photosensitive and can accumulate a dark tarnish if it is exposed to bright light for too long.

Sylvanite is found in Transylvania, from which its name is partially derived. It is also found and mined in Australia in the East Kalgoorlie district. In Canada it is found in the Kirkland Lake Gold District, Ontario and the Rouyn District, Quebec. In the United States it occurs in California and in Colorado where it was mined as part of the Cripple Creek ore deposit. Sylvanite is associated with native gold, quartz, fluorite, rhodochrosite, pyrite, acanthite, nagyagite, calaverite, krennerite, and other rare telluride minerals. It is found most commonly in low temperature hydrothermal vein deposits.