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Formula: (Na,☐)8Nb4(Si4O12)2(O,OH)4.8H2O
Cyclosilicate (ring silicate), labuntsovite group
Crystal System: Orthorhombic
Specific gravity: 2.78 to 2.885 measured, 2.7 calculated
Hardness: 5
Streak: White, very light rose-pink
Colour: Rose-pink, very light pink, light yellow, brown, dark brown due to inclusions
Solubility:
Common impurities: Al,TR,Fe,Mn,Mg,Ba
Environments:
Nenadkevichite occurs in altered and unaltered pegmatites and very rarely in cavities in marble
xenoliths and igneous breccia. It is an alteration product of
epistolite
(Dana).
Localities
At Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Quebec, Canada, nenadkevichite occurs in pegmatites, cavities in
igneous breccia, hornfels and
marble xenoliths in an intrusive alkalic gabbro -
syenite complex. Associated minerals include
microcline, aegirine,
catapleiite, ancylite,
epididymite, eudialyte,
serandite, pectolite,
apophyllite, monteregianite and
vesuvianite
(HOM).
At the type locality, Natrolite Stock, Karnasurt Mountain, Lovozersky District, Murmansk Oblast, Russia, nenadkevichite occurs
between crystals of microcline in a pegmatite rich in
natrolite and albite, in
nepheline syenite
(AM 40.1154, HOM).
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