Tacharanite

Formula: Ca₁₂Al₂Si₁₈O₅₁.18H₂O

Origin of name: from Gaelic tacharan = a changeling, because on standing in air the mineral breaks down to form other compounds (not noticed by later investigators).

Crystal system: Monoclinic

Crystal class: unknown

Twinning:

Unit cell: a = 17.07 Å, b = 3.65 Å, c = 27.9 Å, b = 114.1°

Colour: White, milky white

Diaphaneity: Translucent

Luster: Vitreous to dull

Habit: Massive, cryptocrystalline, porcelanous, as aggregates of fibers to several microns, in bundles or spherulites

Hardness:  5

Specific gravity: 2.21-2.36

Cleavage: 1; {001} perfect

Tenacity: Tough, conchoidal fracture

Streak: White

Synonyms/varieties:

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