Polybasite

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.

History

Discovery date : 1829
Town of Origin : GUARISAMEY, DURANGO
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

Photos:

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
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