Pearceite

Formula: [Ag9CuS4][(Ag,Cu)6(As,Sb)2S7]

Sulfosalt, forms a series with polybasite
Specific gravity: 6.15
Hardness: 3
Streak: Reddish black
Colour: Black with dark red internal reflections
Environments:

Hydrothermal environments

Pearceite occurs in hydrothermal deposits formed at low to medium temperatures associated with acanthite, silver, proustite, quartz, baryte and calcite.

At Pozos, Mexico, pearceite is associated with chalcopyrite.

At Tuscarora, Nevada, USA, pearceite is associated with pyrite.

At the Mangani mine, Sumatra, pearceite occurs on drusy quartz.

At Uchucchacua, Lima department, Peru, pearceite is associated with chalcopyrite, and sometimes proustite.

At Silver Plume, Cochise county, Arizona, USA, pearceite is associated with galena. Separately, pearceite-polybasite twins are scattered on partially resorbed crystals of acanthite after argentite ( a high-temperature variety of acanthite).

At the Rico district, Dolores county, Colorado, USA, pearceite is associated with chalcopyrite and tennantite.

At Smuggler Hill, Lake county, Colorado, USA, pearceite is found as intergrowths with baryte and occasionally with galena or tennantite. Native silver is often found replacing pearceite.

Common impurities: Zn,Fe,Sb