Thomsonite

Formula: NaCa₂Al₅Si₅O₂₀.6H₂O

Origin of name: for T. Thomson (1773-1852), Scottish chemist

Crystal system: Orthorhombic, pseudotetragonal

Crystal class: 2/m 2/m 2/m

Twinning: common on {110} or {041}

Unit cell: a = 13.088, b = 13.052, c = 13.229

Colour: Colourless, white, yellowish, pink, greenish, brown, may be concentrically zoned

Diaphaneity: Transparent to translucent

Luster: Vitreous to somewhat pearly

Habit: Crystals prismatic, acicular or blade-like, striated vertically, rare; lamellar or radiating aggregates, compact

Hardness: 5 to 5.5

Specific gravity: 2.23-2.39

Cleavage: 2; {010} perfect, {100} distinct

Tenacity: Brittle, uneven to subconchoidal fracture

Streak: White

Synonyms/varieties: Thomsonite-Ca, Faröelite, lintonite, mesole, bagotite

Comments: member of the zeolite group. Pyroelectric.