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Formula: Na2KYSi6O15
Cyclosilicate (ring silicate), yttrium-bearing mineral
Crystal system: Orthorhombic
Specific gravity: 2.91 measured, 2.92 calculated
Hardness: 5
Streak: White
Colour: Colourless, white
Luminescence: Fluoresces violet
Common impurities: Y may be replaced by minor REE
Environments
Plutonic igneous rocks
Pegmatites
Localities
At Kvanefjeld deposit, Kuannersuit Plateau, Ilímaussaq complex, Kujalleq, Greenland,
moskvinite-(Y) was discovered in a drill core, where it occurs as a replacement mineral associated with a
britholite group mineral.
The coexistence of an almost pure Y and a light
rare-earth element (REE) (includes Ce and Nd) mineral is interpreted as
fractionation of REE and Y during the replacement of an earlier formed REE mineral. Theoretical calculations of the
observed replacement of feldspathoids by
natrolite show that the generated fluid would have pH greater than 8
(decidedly alkaline), which inhibits large scale mobility of REE. In addition, a K-Fe sulphide mineral for the
first time is observed in Ilímaussaq where it occurs where sodalite is
replaced by natrolite and
arfvedsonite by aegirine.
The sulphide incorporates the S and some of the Cl generated by the alteration of
sodalite, whereas the K and Fe originates from the replacement of
arfvedsonite by aegirine
(MM 80.1.31–41).
At the type locality, Dara-i-Pioz Massif, Districts of Republican Subordination, Tajikistan, moskvinite-(Y)
occurs in a coarse-grained reedmergnerite
pegmatite. Associated minerals include
shibkovite, nordite-(Ce),
leucophanite, microcline,
hyalotekite,
telyushenkoite,
kentbrooksite,
polylithionite and albite.
Moskvinite-(Y) occurs as equant grains up to 2 mm in size with a vitreous lustre
(CM 42.6.1901-1927).
Moskvinite-(Y) from Dara-i-Pioz Massif -
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