pearceite

{{Infobox mineral | name = Pearceite | category = | boxwidth = 24 | boxbgcolor = | image = Pearceite-4jg57a.jpg | caption = Pearceite from Butte, Montana, US | formula = | IMAsymbol = Pea | molweight = 2,096.80 g/mol | strunz = 2.GB.15 (10 ed) 2/E.05-20 (8 ed) | dana = 3.1.8.1 | system = Monoclinic or trigonal | symmetry = Pm1 (no. 164) | color = Black | habit = Pseudohexagonal prisms | twinning = | cleavage = {001} Poor | fracture = Conchoidal to irregular | tenacity = Brittle | mohs = 3 | luster = Metallic | refractive = 2.7 | opticalprop = Biaxial | birefringence = 2.7 | pleochroism = RL Pleochroism (in reflected plane polarised light): Very weak in air, fair in oil | streak = Black | gravity = 6.15 | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Opaque | other = Non-fluorescent, nonmagnetic, not radioactive | references = }} Pearceite is one of the four so-called "ruby silvers", pearceite , pyrargyrite , proustite and miargyrite . 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 , 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.