Class : Sulfides and sulfosalts
    Subclass : Sulfosalts
    Crystal system : Trigonal
    Chemistry : Ag₃AsS₃
    Rarity : Uncommon

Proustite is isomorphic to pyrargyrite, its equivalent to antimony. Rarer than the latter, it constitutes a late primary mineral of silver-bearing hydrothermal deposits, sometimes a supergene mineral of the cementation zone. It is found alongside many other minerals of silver, arsenic, antimony, copper and lead. It was named in honor of Joseph Louis Proust, French chemist and founder of chemical analysis. Most often massive, proustite crystallizes in elongated hexagonal prisms, more rarely in scalenohedra, sometimes in reticulated aggregates. Like pyrargyrite, proustite has an extraordinary metallic luster, associated with a transparency reinforced by its vermilion red to currant red color which earned it its name red silver. But in daylight, it loses this transparency by becoming covered with a gray-black superficial film of acanthite. In museums, samples are often protected from prolonged exposure by a shutter. It is a notable silver ore, although less important than pyrargyrite.

Main photo : Proustite from Chañarcillo, Copiapó, Atacama, Chile © Rock Currier

Twins are known on {10-14} as well as on {10-11}, {0001} and {01-12}.

No fakes listed for this mineral species.