Very rare K-Zr silicate specie Kostylevite in association with a Na-Y-Zr silicate Sazykinaite-(Y). Kostylevite forms colourless to cream coloured crystals. From Koashva Mountain, Khibiny Massif, Kola, Russian Federation. — Photo: David Hospital · CC BY-SA 4.0
Kostylevite
Kostylevite is an IMA-recognized mineral species in the silicate class, with the chemical formula K₂ZrSi₃O₉·H₂O.
It crystallizes in the monoclinic crystal system (space group P2_1/b).
Key properties: Mohs hardness 5; specific gravity 2.74; Vitreous luster; optically biaxial.
IMA symbol Ksv, IMA status: approved, named in 1982.
Found in alkalic pegmatite in a differentiated alkalic massif.
It is found associated with Umbite, wadeite, eudialyte, potassian feldspar, aegirine.
The name refers to Ekaterina Evtikhievna Kostyleva-Labuntsova (1894–1974), Russian mineralogist, Institute of Geology of Ore Deposits, Petrology, Mineralogy, and Geochemistry, Moscow, Russia.