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Formula: Ca2(CaNd)Na3Nb(Si2O7)2(OF)F2
Sorosilicate (Si2O7 groups), rinkite group,
seidozerite supergroup
Crystal system: Monoclinic
Specific gravity: 3.58 measured, 3.608 calculated for the empirical formula
Hardness: 5
Streak: White
Colour: Colourless
Luminescence: does not fluoresce under cathode or ultraviolet light.
Solubility:
Common impurities:
Environments
Nacareniobsite-(Nd) is a new mineral, approved in 2023(?) and to date (April 2025) reported only from the type
locality.
Localities
At the type locality, the Dara-i-Pioz Massif, Districts of Republican Subordination, Tajikistan,
nacareniobsite-(Nd) was found associated with quartz,
pectolite, reedmergnerite,
leucosphenite, baratovite,
aegirine, orlovite,
sokolovaite,
mendeleevite-(Ce),
odigitriaite, pekovite,
zeravshanite, kirchhoffite,
fluorite and garmite.
Nacareniobsite-(Nd) was found in fragments of boulders up to 2m in diameter in the moraine of the Darai-Pioz
glacier. These boulders consist of 90 to 95% medium- to coarse-grained
icy quartz. The characteristic appearance of this rock is determined by
secondary and accessory minerals: large tabular and platy
crystals of golden-brown polylithionite, pink plates of
sogdianite–sugilite, clusters
and tabular grains of pale-orange reedmergnerite, black crystals of
aegirine, orange-brown translucent lenticular crystals of
stillwellite-(Ce), grass-green crystals of
leucosphenite, dark-green columnar crystals of
turkestanite and white crystals of
microcline. Some
quartz-pectolite aggregates
contain many rare and new minerals, including nacareniobsite-(Nd) and those mentioned above as associated
minerals.
Nacareniobsite-(Nd) occurs in a peralkaline (agpaitic)
pegmatite and probably formed at the hydrothermal stage of
pegmatite crystallisation. It occurs as isolated prismatic
grains up to 0.3 mm long and up to 0.03 mm thick embedded in the
quartz-pectolite
aggregate
(CJMP 63.179-190).
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