POLYBASITE

    Class : Sulfides and sulfosalts
    Subclass : Sulfosalts
    Crystal system : Monoclinic
    Chemistry : Ag16Sb2S11
    Rarity : Uncommon

Polybasite is a silver sulfosalt which forms a series with pearceite, its arsenic equivalent. It is a primary mineral of silver hydrothermal deposits where it is associated with other silver sulfides such as stephanite, pyrargyrite or acanthite and quite frequently gold. Its name comes from the Greek polus (many) and basis (base), due to the base-rich chemical composition of this mineral. Polybasite has a metallic luster and an iron black color. It is translucent and dark red in very fine flakes. It forms pseudohexagonal tabular crystals, forming stubby prisms with characteristic triangular striations on the (001) faces. It is locally an important silver ore.

Main photo : Polybasite from Fresnillo, Zacatecas, Mexico © Jeff Scovil

Polybasite from Husky Mine, Yukon, Canada © László Kupi
Polybasite from Imiter, Morocco © Jean-Marc Johannet
Polybasite from Clara Mine, Germany © Stephan Wolfsried
Polybasite from Peyrebrune, Tarn, France © François Garric

Polybasite in the World

The best known samples of polybasite are thick tabular crystals measuring 6 cm from Mexico (Chispas mine, near Arizpe in Sonora), and from mines in the Guanajuato and Fresnillo districts. Good centimeter crystals have also been discovered in the German district of Saxony, in the mines of Freiberg (2.5 cm crystals), Annaberg and Marienberg, as well as in the Canadian Yukon (Husky Mine).

Polybasite in France

In France, polybasite is known in millimeter crystals in Peyrebrune (Tarn), it has also been reported in certain veins around Brioude (Haute-Loire), in Chessy (Rhône), in Poullaouen (Finistère), in Ste-Marie -aux-Mines (Haut-Rhin), in Salsigne (Aude) and in various other localities.

Twinning

No twins known for this mineral species.

Fakes and treatments

No fakes listed for this mineral species.


Hardness : 2.5 to 3
Density : 6.1
Fracture : Conchoidal
Streak : Black

TP : Opaque
RI : -
Birefringence : -
Optical character : Biaxial -
Pleochroism : None
Fluorescence : None

Solubility : Nitric acid

Magnetism : NoneRadioactivity : None

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