Preisingerite, Polybasite-Tac Bi3O(AsO4)2(OH),…

Preisingerite, Polybasite-Tac Bi3O(AsO4)2(OH),…

Preisingerite, Polybasite-Tac

Bi₃O(AsO₄)₂(OH), (Ag,Cu)₆(Sb,As)₂S₇][Ag₉CuS₄   

Locality:

Clara Mine, Rankach valley, Oberwolfach, Wolfach, Black Forest, Baden-Württemberg, Germany

Field of View: 0.65 mm

A creamy white preisingerite aggregate together with tabular pseudohexagonal polybasite-Tac crystals. 

Photo: Michael Förch

Preisingerite is a rare secondary mineral in the oxidized zone of some arsenic-bearing

hydrothermal mineral deposits. Forms translucent white to grey crystals.  

Polybasite-Tac is a polytype of Polybasite, with the same chemical formula but different crystal structure. Polybasite-Tac is therefore classified as an individual mineral species. Polybasite-Tac was previously known as Antimonpearceite, and was renamed by the IMA in 2006.  It is almost always found in known silver deposits.