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Silicate

Tounkite

(Na,Ca,K)₈(Si₆Al₆)O₂₄(SO₄)₂Cl·0.5H₂O
Hardness5–5.5
Crystal systemHexagonal
ClassSilicate
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Tounkite specimen

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

Tounkite

Tounkite is an IMA-recognized mineral species in the silicate class, with the chemical formula (Na,Ca,K)₈(Si₆Al₆)O₂₄(SO₄)₂Cl·0.5H₂O.

It crystallizes in the hexagonal crystal system (space group P6_222). It is a member of the Cancrinite-sodalite structural group.

Key properties: Mohs hardness 5–5.5; specific gravity 2.557; White streak; Vitreous luster; optically uniaxial.

IMA symbol Tou, IMA status: approved, named in 1990.

Replacing lazurite in diopside-lazurite rocks (Malo-Bystrinskoye deposit, Russia); in lazurite calciphyres (Tultuy deposit, Russia).

It is found associated with Diopside, lazurite (Malo-Bystrinskoye deposit, Russia); calcite, diopside, pyrite, apatite (Tultuy deposit, Russia).

The name refers to the Tunka (Tounka) Valley, which is nearby the two deposits.

Index entry. This entry combines official IMA/RRUFF species data with published physical-property data — a full written entry hasn’t been published yet. Browse more T minerals or help write this entry.