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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 02.GB.15
Colour steel black
Crystal system monoclinic
Cleavage poor on (001)
Fracture uneven
Mohs scale hardness 1.5-2
Luster 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.