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Formula: CoSb3
Antimonide of cobalt,
skutterudite subgroup,
non-stoichiometric perovskites group,
perovskite supergroup
Crystal System: Isometric
Specific gravity: 7.2 measured, 7.63 calculated
Hardness: 5 to 5½
Streak: Grey
Colour: Tin-white
Common impurities: Ni,Fe,Cu,Cl
Environments
Localities
At the type locality, the Tunaberg Cu-Co Ore Field, Tunaberg, Nyköping, Södermanland County, Sweden, mineralisation occurs
in a metamorphosed tuffite formation in the upper part of a
volcano-sedimentary sequence metamorphosed to the
upper amphibolite facies. A central zone of
Cu-Co-sulphide skarn ores is hosted by "skarned"
marble, and a peripheral zone of Zn-Pb-sulphide ores hosted by
metamorphosed tuffite, graphitic
slate and marble.
Kieftite was found in polished sections of chalcopyrite-rich ore
collected from dumps and exposed rocks at the abandoned mine, in Cu-Co-sulphide
skarn ores of the central zone. Kieftite forms subhedral to euhedral
crystals up to 400 microns across in aggregates enclosed in chalcopyrite,
that occur associated with bornite,
galena, native bismuth,
native silver, gudmundite and
tetrahedrite. The kieftite may contain inclusions of
chalcopyrite, native bismuth and
dyscrasite. Other minerals identified in kieftite-bearing specimens
include allargentum, antimony,
arsenopyrite, breithauptite,
cobaltite,
costibite/paracostibite,
covellite, cubanite,
electrum, graphite,
molybdenite, nisbite,
safflorite, sphalerite,
stannoidite and uraninite
(CM 32.1.179-183).
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