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Formula: (Na1.5Bi0.5)Ta2O6F
Oxide, microlite group,
pyrochlore supergroup,
bismuth- and tantalum-
bearing mineral
Crystal System: Isometric
Specific gravity: 6.49 measured, 6.568 calculated
Hardness: 5
Streak: White
Colour: Green
Environments
Localities
At the type locality, the Alto Quixaba claim, Quixaba, Frei Martinho, Paraíba, Brazil, the
granitic
pegmatite consists of two different vein-like bodies, each
with limited outcrop. Both pegmatites are discordant with
respect to the biotite schist
host-rock. The first pegmatite vein is sterile and without
economic interest, whereas the second one shows distinctive mineralisation. The main minerals are
perthitic microcline,
quartz and
muscovite, with large amounts of
albite and amblygonite.
Accessory minerals are mainly-blue elbaite,
tantalite-(Fe),
tantalite-(Mn), green beryl
and fluornatromicrolite.
Fluornatromicrolite occurs as regular to flattened octahedral crystals up to 6 mm in size. The colour is
green and the streak is white. The crystals have an adamantine lustre and are transparent in thin fragments
(CM 49.4.1105-1110).
Fluornatromicrolite from the Alto Quixaba claim
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