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
Town of Origin : GUARISAMEY, DURANGO
Country of Origin : MEXIQUE
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°
Hardness : from 2,00 to 3,00
Color : iron black; steel black; black grey
Luster: metallic; adamantine; unpolished
Streak : reddish black; dark red; black
Break : irregular
Cleavage : yes