White crystals of trinepheline associated to fabriesite and jadeite from Myanmar (Tawmaw, Hpakant Township, Mohnyin District, Kachin State, Myanmar). Ex. Erich Laskowski collection (USA). — Photo: David Hospital · CC BY 4.0
Trinepheline
Trinepheline is an IMA-recognized mineral species in the silicate class, with the chemical formula NaAlSiO₄.
It crystallizes in the hexagonal crystal system (space group P6_1).
Key properties: Mohs hardness 5–5.5; specific gravity 2.642; White streak; Vitreous to greasy luster.
IMA symbol Tnph, IMA status: approved, named in 2012.
Found in serpentinized peridotite, replacing jadeite during late stage metamorphism along veins, likely related to decompression.
It is found associated with Nepheline, fabriesite, more rarely with albite, banalsite, stronalsite.
The name refers to the naturally occurring polymorphs of synthetic NaAlSiO4 with a value of the c crystallographic dimension that is three times that of nepheline.