Polybasite with Chalcopyrite Chispas Mine (Pedrazzini mine), Arizpe, Mun. de Arizpe, Sonora, Mexico Miniature, 5.5 x 4.3 x 3.2 cm “Courtesy of Rob Lavinsky, The Arkenstone, www.iRocks.com”
Chemical Formula: [(Ag,Cu)6(Sb,As)2S7][Ag9CuS4]
Name Origin: From the Greek, poly, “many” and basis, “a base” in allusion to the basic character of the compound.

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.


Discovery date : 1829
Country of Origin : MEXIQUE

Optical properties

Optical and misc. Properties: Translucide  –   Opaque
Reflective Power: 30,2-31,7% (580)
Refractive Index: from 2,72 to 2,73
Axial angle 2V : 22°

Physical properties

Hardness : from 2,00 to 3,00
Density: 6,10
Color : iron black; steel black; black grey
Luster: metallic; adamantine; unpolished
Streak : reddish black; dark red; black
Break : irregular
Cleavage : yes


Silver, Polybasite 2.0×1.2×0.9 cm Highland Bell Mine, Beaverdall British Columbia, Canada Copyright © David K. Joyce Minerals
Acanthite on Polybasite San Carlos Vein, Proano Mine, Fresnillo District, Zacatecas, Mexico Cabinet, 10.3 x 7.5 x 6.5 cm “Courtesy of Rob Lavinsky, The Arkenstone, www.iRocks.com”
Proustite, Polybasite 4.8×4.2×2.7 cm Imiter Mine, Imiter District Djebel Saghro (Jbel Saghro), Ouarzazate Province Morocco Copyright © David K. Joyce Minerals