Freibergite

Infobox mineral
name = Freibergite
category = Mineral: sulfosalt
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formula = Cu₁₂Sb₄S₁₃
molweight = 1,929.46 gm
color = Steel gray to Black
habit = massive to well formed crystals
system = Cubic
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cleavage = None
fracture = Uneven
tenacity =
mohs = 3½ - 4
luster = Metallic
streak = reddish black
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diaphaneity = Opaque
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Freibergite is a complex sulfosalt mineral of silver, copper, iron, antimony and arsenic with formula (Ag,Cu,Fe)₁₂(Sb,As)₄S₁₃. It has cubic crystals and is formed in hydrothermal deposits. It forms one solid solution series with tetrahedrite and another with argentotennantite. Freibergite is an opaque, metallic steel grey to black and leaves a reddish black streak. It has a Mohs hardness of 3.5 to 4.0 and a specific gravity of 4.85 - 5. It is typically massive to granular in habit with no cleavage and an irregular fracture.

The mineral was first described in 1853 from an occurrence in the silver mines of the type locality at Freiberg, Saxony.

References

* [http://rruff.geo.arizona.edu/doclib/hom/freibergite.pdf Mineral handbook]
* [http://webmineral.com/data/Freibergite.shtml Webmineral]
* [http://www.mindat.org/min-1605.html Mindat]