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.
