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Formula: (Pb,☐)2Ta2O6[☐,(OH),O]
Oxide, microlite group,
tantalum-bearing mineral
Crystal System: Isometric
Specific gravity: 7.310 to 7.832 measured, 7.122 calculated
Hardness: 6
Streak: White
Colour: Yellowish brown
Luminescence: No fluorescence under UV
Environments
Kenoplumbomicrolite was approved by IMA as a valid, new species in 2016. To date (June 2023) it has been
reported only from the type locality.
Localities
At the type locality, Ploskaya Mt, Western Keivy Massif, Keivy Mountains, Lovozersky District, Murmansk Oblast, Russia,
kenoplumbomicrolite occurs in an amazonite
pegmatite. It forms yellowish brown octahedral, cuboctahedral
and massive crystals, up to 20 cm. Attempts to measure density were affected by the ubiquitous presence of
uraninite inclusions
(MM 82.1049-1055).
The vein was confined to the contact between gneiss and
schist. The vein contact zone consists of fine-grained
albite and is succeeded nearer the centre by an indistinct zone of
amazonite blocks up to 2.5 m in size and partly replaced by
albite. The quartz core has
galena pockets up to 0.4 m, coarse
biotite flakes and cleavelandite
aggregates. Other associated minerals are zinnwaldite,
anglesite, bastnäsite-(Ce),
bismite, bismuth,
bismuthinite, bismutite,
cassiterite,
caysichite-(Y),
churchite-(Y),
columbite-(Mn), emplectite,
fergusonite-(Y), fluorite,
gadolinite-(Y), gahnite,
galena, hingganite-(Y),
hingganite-(Yb),
kainosite-(Y),
kamphaugite-(Y), kasolite,
keiviite-(Y), keiviite-(Yb),
kuliokite-(Y), lanarkite,
leadhillite, löllingite,
monazite-(Ce),
pyromorphite, scotlandite,
sillénite, sphalerite,
tengerite-(Y),
thalénite-(Y), thorite,
uraninite,
vyuntspakhkite-(Y),
wulfenite, xenotime-(Y),
xenotime-(Yb) and zavaritskite.
The mineral “plumbomicrolite” was identified in this vein in 1975, but according to the IMA-approved rules for
nomenclature the name “plumbomicrolite” must be preceded by the prefix “keno,” which indicates that the Y site is
dominantly vacant
(AM 106.1189).
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