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Formula: NaAlSiO4
Tectosilicate (framework silicate), feldspathoid group,
paramorph of nepheline
Crystal System: Hexagonal
Specific gravity: 2.642 calculated
Hardness: 5 to 5½
Streak: White
Colour: White to pale yellow
Luminescence: Not fluorescent in UV
Common impurities: Ca,K
Environments
Localities
At the type locality, Tawmaw, Hpakant-Tawmaw Jade Tract, Hpakant Township, Mohnyin District, Kachin State, Myanmar,
two new (in 2012) mineral species, trinepheline and fabrièsite, are
described from serpentinised
peridotite, replacing jadeite
during late stage metamorphism along veins of the deposit. Trinepheline is known for the polymorphs of synthetic
NaAlSiO4 with a value of the c parameter that is three times that of
nepheline, hence the name "trinepheline".
Fabrièsite and trinepheline occur intimately intergrown together with
nepheline, more rarely with albite
and other feldspar group phases such as
banalsite and stronalsite; other
associated minerals are jadeite and
secondary products like
natrolite and harmotome. Both
fabrièsite and trinepheline are
pseudomorphous after jadeite and
occur as skeletal allotriomorphic (not having their own regular shape, as determined by their internal structure, but
being shaped instead by adjacent minerals) crystals up to 15 to 20 μm long and 5 to 10 μm wide. They are white to
yellowish in hand specimens and colourless in thin section; the streak is white and the lustre appears vitreous to
greasy
(EJM 26.257-263, HOM).
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