Bluish-green tounkite with bright sulphur-yellow bystrite and blue lazurite in white calcite matrix from the type locality for both species (Malo-Bystrinskoe, Malaya Bystraya River Valley, Lake Baikal, Irkutsk Oblast, Russian Federation). Bystrite and tounkite are very rare silicates. Ex. Erich Laskowski collection (USA). — Photo: David Hospital · CC BY 4.0
Bystrite
A sulfur-bearing member of the cancrinite group, probably named for Russia's Malaya Bystraya deposits.
Intro adapted from Wikipedia (CC BY-SA).
Bystrite is an IMA-recognized mineral species in the silicate class, with the chemical formula (Na,K)₇Ca(Si₆Al₆)O₂₄(S²⁻)₁.₅·H₂O.
It crystallizes in the hexagonal crystal system (space group P31c). It is a member of the Cancrinite-sodalite structural group.
Key properties: Mohs hardness 5; specific gravity 2.43; Vitreous luster; refractive index 1.622; optically uniaxial.
IMA symbol Bys, IMA status: approved, named in 1990.
Occurs as metasomatic lenses in dolomitic marble.
It is found associated with Lazurite, diopside, calcite, pyrite.
Presumably for the occurrence in the Malaya Bystraya deposit, Russia.