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Formula: BiMo6+(2-5x)Mo5+6xO7(OH).H2O (0 < x < 0.4)
Hydrated molybdate,
bismuth-bearing mineral
Crystal system: Monoclinic
Specific gravity: 5.114 calculated
Hardness: 3
Streak: White
Colour: Yellow, yellowish green, pale blue, colourless
Luminescence: Not fluorescent
Environments
Plutonic igneous environments
Hydrothermal environments
Gelosaite is a secondary mineral formed in the
oxidation zone of
bismuth-molybdenum deposits.
Localities
At Kingsgate, Gough Co., New South Wales, Australia, mineralisation is largely confined to
quartz-rich pipes in
leucogranite. Gelosaite was originally recovered from a single
boulder of quartz from the waste dumps of the Old 25 pipe. Crystals up to
0.5 mm in size are tabular and range in colour from pale yellow and greenish yellow to pale blue. These occur perched
on quartz crystals in vugs associated with
bismutite. Nearly all gelosaite crystals from this locality are
twinned
(AM 96.268-273).
Gelosaite from Kingsgate - Image
At the type locality, Punta de Su Seinargiu, Sarroch, Metropolitan City of Cagliari, Sardinia, Italy, the deposits
are related to leucogranitic intrusions. The only
primary
molybdenum-bearing mineral is
molybdenite, associated with
pyrite, bismuthinite, and
sphalerite in quartz veins
ranging from 5 to 15 cm thick and more rarely in the granite itself.
Study of samples collected from small dumps yielded in addition
native bismuth, cassiterite,
anatase, brookite,
aeschynite-(Ce),
synchysite-(Ce),
xenotime-(Y), bismoclite,
ferrimolybdite,
koechlinite, wulfenite,
powellite and muscovite.
Only three small samples of gelosaite were found at the type locality, where it occurs in cavities in
quartz veins within a granite
rock. Gelosaite is a secondary mineral formed in the
oxidation zone and is associated with sardignaite,
ferrimolybdite,
koechlinite, wulfenite and
muscovite. It occurs as prismatic and very thin, elongated and tabular
crystals up to 1 mm in length and a few micrometers across. Twinning was not observed in material from this locality
(AM 96.268-273).
Gelosaite from Punta de Su Seinargiu -
Image
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