Cosalite - Encyclopedia

    Class : Sulfides and sulfosalts
    Subclass : Sulfosalts
    Crystal system : Orthorhombic
    Chemistry : Pb2Bi2S5
    Rarity : Uncommon


Cosalite is a relatively common mineral found in mid-temperature Pb-Bi hydrothermal veins and contact metamorphism deposits. It owes its name to its discovery location : the Nuestra Señora mine near Cosala (Mexico). It sometimes appears in prismatic crystals, frequently fibrous to acicular and capillary by elongation according to [001], but most often remains massive, constituting fibrous or feathery aggregates with a radiated texture. With a metallic luster, cosalite has a lead gray to steel gray color. It is an occasional bismuth ore.

Main photo : Cosalite from Luserna Stone Quarries, Piedmont, Italy © Beppe Finello

Cosalite in the World

Beautiful crystals come from the Nordmark deposit (Sweden). Good samples are also reported from several American mines in Arizona (Magma), California (Darwin), and Colorado (Red Mountain), as well as from the Transylvania gold deposits in Romania (Cavnic, Moravita).

Cosalite in France

In France, cosalite is reported in numerous deposits such as Chessy (Rhône), the Chizeuil mine (Saône-et-Loire), in Ste-Marie-aux-Mines (Haut-Rhin), in St-Yrieix-la- Perche (Haute-Vienne), in Salsigne (Aude), at Kaymar (Aveyron), etc...
 
Right photo : Cosalite de Lauriéras, Saint-Yrieix-la-Perche, Haute-Vienne, France © Pierre Le Roch

Twinning

No twin known for this mineral species.

Fakes and treatments

No fake identified for this mineral species but can be difficult to visually differentiate from other metallic minerals.



Hardness : 2.5 to 3
Density : 6.8 to 7
Fracture : Irregular
Streak : Black


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


Solubility : Nitric acid


Magnetism : None
Radioactivity : None

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