Formula: CoAsS
Sulphide of cobalt and arsenic, forms a series with gersdorffite
Specific gravity: 6.33
Hardness: 5½
Streak: Greyish black
Colour: Reddish silver white, violet steel gray, or black.
Common impurities: Cu,Pb,Sb,Fe,Ni

Metamorphic environments
Hydrothermal environments

Cobaltite is a secondary mineral that occurs in high-temperature hydrothermal deposits, as disseminations, and as veins in contact metamorphosed rocks (HOM, Webmin). Associated minerals include allanite, calcite, chalcopyrite, magnetite, scapolite, skutterudite, sphalerite, titanite and zoisite (Mindat).

At Neudorf in the Hartz mountains, Germany, cobaltite occurs in tetrahedrite - tennantite, and also as inclusions in galena (Minrec 43.1.32).

At Tunaberg, Sweden, cobaltite is associated with magnetite, sphalerite, chalcopyrite, skutterudite, allanite, zoisite, scapolite, titanite and calcite (HOM).

At the Dolgellau Gold-belt, Gwynedd, Wales, UK, cobaltite ocurs in high to medium temperature veins where it is early in the paragenesis. It is associated with arsenopyrite and pyrite, and often overgrown by, and forms inclusions in, later base-metal sulphides such as pyrrhotite, sphalerite, chalcopyrite and galena. It often has a coating of supergene erythrite (MW).

At the Blackbird mine, Lemhi county, Idaho, USA, cobaltite occurred as microscopic grains in quartz with tourmaline and cobalt-rich arsenopyrite; crystals to 5mm were also found disseminated in quartz, associated with biotite, chlorite and apatite (Minrec 41.4.362).

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