Pinkish white acicular crystals of mountainite associated to brown manganneptunite. From: Yubileinaya Pegmatite, Lovozero Massif, Kola, Russian Federation. — Photo: David Hospital · CC BY-SA 4.0
Mountainite
Mountainite is an IMA-recognized mineral species in the silicate class, with the chemical formula KNa₂Ca₂[Si₈O₁₉(OH)]·6H₂O.
It crystallizes in the monoclinic crystal system (space group P2/c).
Key properties: Mohs hardness 3; specific gravity 2.36; Silky luster; optically biaxial.
IMA symbol Mtn, grandfathered status — known before the IMA’s founding, named in 1957.
Found in a kimberlite pipe (Kimberley, South Africa); in a differentiated alkalic massif (Lovozero massif, Russia).
It is found associated with Rhodesite (Kimberley, South Africa); natrolite, steenstrupine, chkalovite, neptunite, s¶erandite, aegirine, leucosphenite, zorite, raite, polylithionite.
The name refers to Edgar Donald Mountain, Professor of Geology, Rhodes University, Grahamstown, South Africa.