Formula: NaCa₂[Al₅Si₅O₂₀] · 6H₂O

Species:

Colour: Colourless, white, light yellow, light green, pink, brown

Lustre: Vitreous, Pearly

Hardness: 5 – 5½

Specific Gravity: 2.23 – 2.29

Crystal System: Orthorhombic

Member of: Thomsonite Subgroup > Zeolite Group

Name: Renamed in 1820 by Henry James Brooke in honor of Thomas Thomson [April 12, 1773 Crieff, Perthshire, Scotland – July 2, 1852 Kilmun, Argyleshire, Scotland], professor of chemistry at the University of Glasgow. Thomson was an indefatigable mineral chemist and contributed enormously to the number of accurate chemical analyses of minerals during his career as well as having discovered many new mineral species. The suffix -Ca denotes the dominance of calcium in the mineral.

Type Locality: Old Kilpatrick, West Dunbartonshire – Scotland, UK

Zeolite Group: The calcium analogue of Thomsonite-Sr.

Some habits may be confused with stellerite.