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Formula: Cu2(UO2)2(VO4)2(OH)2.6H2O
Hydrated vanadate, uranyl
mineral, carnotite group
Crystal System: Monoclinic
Specific gravity: 4.05 measured, 4.1 calculated
Hardness: 2½
Streak: Light green
Colour: Olive-green, yellowish green
Solubility: Soluble in acids
Very strongly RADIOACTIVE
Environments
Sengierite is an uncommon secondary mineral
deposited from solutions derived from altering uraninite
(Mindat).
Localities
At the type locality, the Luiswishi Mine, Kawama, Kipushi Territory, Haut-Katanga, DR Congo, an unusual
radioactive mineral has been found in fissures cutting an argillaceous
(clay-like) phase. This portion of the
deposit consists essentially of chlorite and
talc. Sengierite occurs as small, green, platy crystals that have
a vitreous lustre and coat fracture surfaces in a flake-like fashion. The fissures containing the crystals
occur along a fault and the siegenite is accompanied by black oxides containing
iron, copper,
cobalt and nickel and also
some lustrous yellow volborthite. Less frequently it is found
associated with vandenbrandeite, fibrous
malachite, garnierite (a green nickel ore which has formed as a
result of lateritic weathering of
ultramafic rocks)
and chrysocolla.
Pitchblende is also found in small pockets along the fault where it
has been partly altered to vandenbrandeite and
kasolite. The sengierite is believed to be of
supergene origin produced by deposition from solutions
containing uranium, vanadium
and copper derived from earlier minerals
(AM 34.109-120).
At the Cole Mine, Bisbee, Cochise County, Arizona, USA, sengierite was discovered in a small pod of
massive chalcocite in one of five sulphide-oxide veins; minor
amounts of malachite were also found in this vein. The veins were
in a very compact limestone, and the ore was a mixture of
chalcocite, covellite
and malachite, with pockets of
chlorargyrite. Uranium
mineralisation was present in the limestone as
tyuyamunite which occurred as small yellow crystals lining cracks
and fissures in the limestone adjacent to the massive
chalcocite-covellite
ore bodies.
Sengierite occurs in small pockets and patches up to 20 mm across, as quite minute rhombic-shaped
platelets, the longer diagonals of which do not exceed 0.03 mm, but average less than 0.02 mm
(AM 42.408–411).
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