Outsatnding sharp pale tan prismatic hexagonal crystals of the mineral kalsilite, from: Löhley, Üdersdorf, Eifel, Rhineland-Palatinate, Germany. — Photo: David Hospital · CC BY-SA 4.0
Kalsilite
A vitreous white-to-gray potassium feldspathoid of potassium-rich lavas, hardness about 5.5.
Intro adapted from Wikipedia (CC BY-SA).
Kalsilite is an IMA-recognized mineral species in the silicate class, with the chemical formula KAlSiO₄.
It crystallizes in the hexagonal crystal system (space group P31c). It is a member of the Tridymite-Nepheline structural group.
Key properties: Mohs hardness 6; specific gravity 2.59–2.62; Vitreous to greasy luster; optically uniaxial.
IMA symbol Kls, grandfathered status — known before the IMA’s founding, named in 1942.
Found in the groundmass of some potassium-rich and silica-deficient lavas and tuffs; rare in syenites; may be formed by the breakdown of silica-rich leucite in alkalic ultramafic rocks; from a granulite-facies emery deposit.
It is found associated with Olivine, melilite, clinopyroxene, phlogopite, nepheline, leucite.
The name refers to potassium, Kalium, ALuminum, and SILicate in the composition.