Pearceite

Pearceite is one of the four so-called "ruby silvers", pearceite Cu(Ag,Cu)₆Ag₉As₂S₁₁, pyrargyrite Ag₃SbS₃, proustite Ag₃AsS₃ and miargyrite AgSbS₂. It was discovered in 1896 and named after Dr Richard Pearce (1837–1927), a Cornish–American chemist and metallurgist from Denver, Colorado.

Nomenclature

Pearceite and polybasite are closely related minerals that form the pearceite-polybasite series. Originally pearceite was thought to be an arsenic analogue of polybasite Cu(Ag,Cu)₆Ag₉Sb2S₁₁, and was called arsenpolybasite, and one polytype of polybasite was called antimonpearceite. Arsenpolybasite was found to represent two different polytypes, arsenpolybasite-221 and arsenpolybasite-222. In modern usage the old name pearceite is replaced by the polytype name pearceite-Tac, arsenpolybasite-221 by pearceite-T2ac, arsenpolybasite-222 by pearceite-M2a2b2c and antimonpearcite by polybasite-Tac. Pearceite-Tac forms a series with polybasite-Tac.

Crystallography and Structure

Two structural varieties, trigonal and monoclinic, are known. The trigonal variety crystallises in the hexagonal scalenohedral class 3m (3 2/m), space group P3m1 (P3 2/m 1). The monoclinic variety crystallises in the prismatic 2/m class, space group C2/m.