Tokkoite

Formula: K₂Ca₄Si₇O₁₇(O,OH,F)₄

Origin of name: after locality Tocco River, Russia

Crystal system: Triclinic

Crystal class: 1

Twinning:

Unit cell: a = 10.438, b = 12.511, c = 7.112, α = 89.92°, β = 99.75°, γ = 92.89°

Colour: Light brown to pale yellow

Diaphaneity: Transparent

Luster: Vitreous

Habit: Columnar aggregates, radiating structure

Hardness: 4 to 5

Specific gravity: 2.76

Cleavage: 2; {010} perfect, {110} less perfect

Tenacity: Splintery fracture

Streak: White

Synonyms/varieties:

Comments: isostructural with tinaksite