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Formula: (Na,Ca,U)2(Ta,Nb)2O6(O,F)
Oxide, uranium-, tantalum- and
niobium- bearing mineral
Crystal system: Isometric
Specific gravity: 6.580 measured, 6.506 calculated
Hardness: About 5
Streak: Yellowish brown
Colour: Brown or yellowish brown
Common impurities: Ca,U,Nb,H2O,F
RADIOACTIVE
Environments
Localities
At the type locality, Pegmatite vein no. 309, Guanpo pegmatite field, Guanpo, Lushi County, Sanmenxia, Henan,
China, oxynatromicrolite was found in the rare metal
granitic
pegmatite vein. It occurs as strongly
metamict, and mostly euhedral, octahedral crystals up to 0.2 mm across. Oxynatromicrolite crystallised
during the late stage of formation of the pegmatite dyke
and is associated with quartz,
albite, K-feldspar,
muscovite, kaolinite,
tantalite-(Mn),
stibiotantalite,
pollucite, spodumene,
montebrasite, hafnium-rich
zircon, a red tourmaline,
polylithionite,
trilithionite,
luanshiweiite and a hydrated derivative of oxynatromicrolite
(MM 81.4.743-751).
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