Freibergite

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 to 5. It is typically massive to granular in habit with no cleavage and an irregular fracture.

Freibergite
General
Category	Sulfosalt minerals
Formula	Cu12Sb4S13
IMA symbol	Fb[1]
Strunz classification	2.GB.05
Crystal system	Cubic
Crystal class	Hextetrahedral (43m) H-M symbol: (4 3m)
Space group	I43m
Identification
Formula mass	1,929.46 g/mol
Color	Steel gray to black
Crystal habit	massive to well formed crystals
Cleavage	None
Fracture	Uneven
Mohs scale hardness	3.5–4
Luster	Metallic
Streak	reddish black
Diaphaneity	Opaque

Not to be confused with Frohbergite.

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