Oxybismutomicrolite

oxybismutomicrolite

bismutotantalite

cheralite

monazite-(Ce)

Images

Formula: (Bi1.330.67)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

Pegmatites

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 albitelepidoliteelbaite 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).

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