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Polybasite - Arizpe, Sonora, Mexico.jpg
Locality: Arizpe, Sonora, Mexico. Scale bar is one inch (2.5 cm.)
Category Sulfosalt minerals
(repeating unit)
Strunz classification 2.GB.15
Crystal system Monoclinic and trigonal polytypes
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group C2/c
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 [1][2][3][4]

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.


  1. ^ Polybasite: mindat.org
  2. ^ Webmineral.com
  3. ^ Handbook of Mineralogy
  4. ^ Rudolf Dǔd'a and Luboš Rejl (1990). Minerals of the World. Arch Cape Press. p. 40. ISBN 0-517-68030-0. 
Unusual polybasite specimen from Mayo Mining District, Yukon Territory, Canada. Size 3.0 x 2.2 x 1.3 cm.