Polybasite

Polybasite
General
Category	Sulfosalt minerals
Formula (repeating unit)	[(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]

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

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.

References

1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi: 10.1180/mgm.2021.43 . S2CID   235729616.
2. Polybasite: mindat.org
3. Webmineral.com
4. "Handbook of Mineralogy" (PDF). Archived from the original (PDF) on 2016-03-03. Retrieved 2011-05-16.
5. Rudolf Dǔd'a and Luboš Rejl (1990). Minerals of the World. Arch Cape Press. p. 40. ISBN   0-517-68030-0.