Polybasite

sulfosalt

hydrothermal

Formula: [Ag9CuS4][(Ag,Cu)6(Sb,As)2S7]
Sulfosalt, pearceite-polybasite group, forms a series with pearceite.
Specific gravity: 6.1
Hardness: 2½ to 3
Streak: Black
Colour: Black with dark ruby red internal reflections
Environments:

Hydrothermal environments

Polybasite occurs in silver veins of low to moderate temperature of formation, associated with pyrargyrite, tetrahedrite, stephanite, other silver sulfosalts, acanthite, gold, quartz, calcite, dolomite and baryte (HOM).

In the Imiter district, Morocco, polybasite occurs on a quartz-rich vein matrix in a late silver assemblage, associated with proustite. It is best developed in the dolomite cavities. Sometimes crystals of imiterite rest on polybasite crystals, and polybasite sometimes forms a substrate for acanthite crystals (MinRec 42.2.126-127).

At the Caribou mine, Boulder county, Colorado, USA, polybasite has been found partially replaced by stephanite (R&M 87.4.313).

At the Smuggler mine, Boulder county, Colorado, USA, a specimen has been found with crystals of polybasite scattered across a plate of milky quartz crystals. The polybasite crystals are partially coated with and altered to pseudomorphs of silver and acanthite after the high temperature form of silver sulphide known as argentite (R&M 87.4.323).

At Silver Plume, Clear Creek county, Colorado, USA, polybasite twins have been found scattered across partially resorbed crystals of pseudomorphs of acanthite after the high temperature form of silver sulphide known as argentite (R&M 87.4.311).

At the Eldorado Mine, Ouray county, Colorado, USA, polbasite has been found with pyrargyrite as small intergrown masses with base-metal sulphides. It also occurred as microcrystals associated with chalcopyrite and pyrargyrite (R&M 84.5.424).

At the Red Mountain district, Ouray county, Colorado, USA, polybasite has been found partially coated with and replaced by pseudomorphs of silver and acanthite after the high temperature form of silver sulphide known as argentite (R&M 87.4.326).

Common impurities: As,Fe

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