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Formula: CuCo2S4. The valence state of copper is Cu+ and the electronic formula is
Cu1.2+(Co2.4+)2(Si1.4-)4 (CM 46.1317-1322).
Sulphide, carrollite subgroup,
thiospinel group,
spinel supergroup,
cobalt-bearing
mineral
Crystal System: Isometric
Specific gravity: 4.5 to 4.8 measured, 4.83 calculated
Hardness: 4½ to 5½
Streak: Grey-black
Colour: Bright silver
Luminescence: Not fluorescent under UV
Common impurities: Ni
Environments
Carrollite occurs in hydrothermal vein deposits. Associated minerals include
tetrahedrite, linnaeite,
siegenite, polydymite,
chalcopyrite, bornite,
digenite, djurleite,
chalcocite, pyrrhotite,
pyrite, sphalerite,
millerite, gersdorffite,
ullmannite and cobalt-bearing
calcite
(HOM).
Localities
At the Kamoya South II Mine, Kamoya, Kambove District, Haut-Katanga, DR Congo, carrollite is frequently
etched, due to weathering in the oxidised or transition zone. Only crystals from below the transition zone escape
etching. Carrollite in the oxidised zones may be completely converted to
asbolane, heterogenite or
spherocobaltite. Vugs with lightly or partially etched
carrollite sometimes have late chalcocite,
cobalt-bearing calcite, or
cobalt-bearing dolomite in
addition to malachite and/or
chrysocolla.
Late carrollite deposition has been observed on chalcopyrite
and some carrollite crystals
(R&M 84.4.364).
Carrollite from the Kamoya South II mine -
Image
At the type locality, the Patapsco Mine, Patapsco Mines, Finksburg, Carroll county, Maryland, USA, mineralised
veins appear in quartz -
chlorite - biotite
schist, whereas the waste dumps at the mines consist of
hornblende - biotite
schist containing scattered
magnetite crystals. Minerals include disseminated
bornite, carrollite,
chalcocite, chalcopyrite,
magnetite, pyrite and
quartz
(R&M 97.2.188).
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