Polybasite

Polybasite is a sulfosalt mineral of silver, copper, antimony and arsenic. Its chemical formula is [(Ag,Cu)₆(Sb,As)₂S₇][Ag₉CuS₄].

Polybasite
General
Category	Sulfosalt minerals
Formula	[(Ag,Cu)6(Sb,As)2S7][Ag9CuS4]
IMA symbol	Plb[1]
Strunz classification	2.GB.15
Crystal system	Monoclinic and trigonal polytypes
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	C2/c
Identification
Colour	steel black
Cleavage	poor on (001)
Fracture	uneven
Mohs scale hardness	1.5–2
Lustre	metallic, adamantine or glimmering
Streak	black with reddish tint
Specific gravity	6–6.2
References	[2][3][4][5]

It forms black monoclinic crystals (thin, tabular, with six corners) which can show dark red internal reflections. It has a Mohs hardness of 2.5 to 3. It is found worldwide and is an ore of silver. The name comes from the number of base metals in the mineral.

Images

• 
  Unusual polybasite specimen from Mayo Mining District, Yukon Territory, Canada.