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Formula: Bi2Se2Te
Valence: Bi3+2Se2-2Te2-
Selenide-telluride of
bismuth, tetradymite group
Crystal System: Trigonal
Specific gravity: 7.94 calculated for the ideal formula, 7.80 calculated for the empirical formula
Hardness: 2ġ
Streak: Black
Colour: Steel-grey
Common impurities: Cu,Pb,S
Environments
Plutonic igneous environments
Hydrothermal environments
Localities
The type locality is the Otish Mountains U deposit, Otish Mountains, Baie-James, Jamésie, Nord-du-Québec, Québec,
Canada. Uranium vein-type deposits located in the Otish Mountains basin are
associated with strongly albitised
doleritic dykes and sills. Two periods of mineralisation were
recognised. The first, contemporaneous with the albitisation, consists
of brannerite and uraninite. The
second, separated from the previous by tectonic movements, is characterised by
dolomite, and a complex association of
selenides, tellurides and
sulphides including skippenite, watkinsonite,
poubaite, součekite,
clausthalite, aikinite,
wittichenite, molybdenite,
pyrite, chalcopyrite,
galena, digenite,
covellite, electrum and
native bismuth.
Skippenite is associated with bismuth
selenides whose composition is close to Bi2(Se,Te,S)2
and (Bi,Pb)2(Se,Te,S)3. Skippenite is the most abundant
selenide in the deposit. It occurs as massive aggregates of lamellar crystals,
0.2 to 1 mm in length, intimately associated with watkinsonite
(CM 25.4.625-638).
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