Red glassy raslakite is nepheline-syenite. Rare eudyalite group mineral, occurs only at 2 places worldwide, this one from the type locality: Karnasurt Mountain, Lovozero Massif, Northern Region, Russian Federation. — Photo: David Hospital · CC BY-SA 4.0
Raslakite
A rare eudialyte-group mineral with cyclic silicate groups.
Intro adapted from Wikipedia (CC BY-SA).
Raslakite is an IMA-recognized mineral species in the silicate class, with the chemical formula Na₁₅Ca₃Fe₃(Na,Zr)₃Zr₃(Si,Nb)Si₂₅O₇₃(OH,H₂O)₃(Cl,OH).
It crystallizes in the hexagonal crystal system (space group R3). It is a member of the Eudialyte structural group.
Key properties: Mohs hardness 5; specific gravity 2.95; White streak; Vitreous luster; refractive index 1.61; optically uniaxial.
IMA symbol Rsk, IMA status: approved, named in 2002.
Found in an agpaitic pegmatite in an alkaline igneous complex.
It is found associated with Microcline, aegirine, nepheline, lamprophyllite, kazakovite, terskite, fluorcaphite.
The name refers to the Raslak cirque, which is nearby the type locality.