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Formula: (Bi1.33☐0.67)Σ2Ta2O6O
Oxide, microlite group, bismuth-
and tantalum- bearing mineral
Specific gravity: 6.98 measured, 7.056 calculated
Hardness: 5
Streak: Greyish white
Colour: Black
Luminescence: No fluorescence in UV
Solubility: Does not react with cold hydrochloric or nitric acid
Environments
Localities
At the Scherlovyi pegmatite near Taiginka village, Kyshtym, Chelyabinsk Oblast, Russia, a mineral corresponding by
chemical composition to oxybismutomicrolite has been reported as dark brown resinous grains up to 2 mm embedded
in the granitic
pegmatite, and associated with
beryl, bismuth,
bismutocolumbite,
cheralite, fluorapatite,
fluor-schorl, gahnite,
hercynite, magnetite,
columbite-(Mn),
monazite-(Ce), rutile,
spessartine, xenotime-(Y)
and zircon
(AM 106 1189-1190).
At the type locality, the Solnechnaya pegmatite, Malkhan pegmatite field, Krasnyi Chikoy, Krasnochikoysky District,
Zabaykalsky Krai, the central part of the vein is composed of the K-feldspar
graphic pegmatite with blocky aggregates of
K-feldspar and quartz up to 1 m
across. A miarolitic cavity (3 × 2.5 × 1.5 m) was uncovered in 1985. The walls of the cavity were overgrown by
excellent druses of smoky quartz up to 50 × 25 cm, gemmy crystals of
watermelon tourmaline up to 18 × 15 cm, and perfect crystals of
cleavelandite and lepidolite.
Oxybismutomicrolite was found in this cavity as black octahedral crystals up to 1 mm and equant grains up to
2 mm embedded in
albite–lepidolite–elbaite matrix in association with native
bismuth, bismutite,
bismutotantalite,
fluorapatite, fluorite,
fluornatromicrolite,
pollucite, stibiotantalite,
topaz, xenotime-(Y) and
hafnium-rich zircon.
Most of “microlite” grains are zonal with different zones representing solid-solution series between
fluornatromicrolite and oxybismutomicrolite
(MM 84.444-454, AM 106 1189-1190).
Oxybismutomicrolite from the Malkhan pegmatite
field - Image
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