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Formula: CoAsS
Sulphide of cobalt and arsenic,
cobaltite group, forms
a series with
gersdorffite
Crystal System: Orthorhombic
Specific gravity: 6.33 measured, 6.335 calculated
Hardness: 5½
Streak: Greyish black
Colour: Reddish silver white, violet steel gray, or black.
Common impurities: Cu,Pb,Sb,Fe,Ni
Environments:
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).
Localities
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).
Cobaltite from Tunaberg - Image
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).
Cobaltite from the Blackbird Mining District -
Image
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