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Vishnevite
The sulfate member of the cancrinite group — a hexagonal feldspathoid of alkaline rocks.
Intro adapted from Wikipedia (CC BY-SA).
Vishnevite is an IMA-recognized mineral species in the silicate class, with the chemical formula Na₈(Al₆Si₆)O₂₄(SO₄)·2H₂O.
It crystallizes in the hexagonal crystal system (space group P6_3). It is a member of the Cancrinite, Cancrinite-sodalite structural group.
Key properties: Mohs hardness 5–6; specific gravity 2.32–2.42; refractive index 1.495; optically uniaxial.
IMA symbol Vhn, grandfathered status — known before the IMA’s founding, named in 1944.
Found in poikilitic aegirine-nepheline-sodalite syenites and associated pegmatites.
It is found associated with Aegirine, nepheline, cancrinite, sodalite, scolecite.
The name is derived from the locality in the Vishnevy Mountains, Russia.