CHEMISTRY NaCa2Al5Si5O20.6H2O
CRYSTALLOGRAPHY Orthorhombic (pseudo tetragonal)
CRYSTAL GROWTH AND HABITS Thomsonite normally is acicular or fibrous and occurs as radiating spherical masses. It can also be columnar aggregates or be botryoidal or massive.
COLOR AND OTHER OPTICAL PROPERTIES Transparent to translucent and commonly white in color with various shades of yellow or pink; sometimes brownish or greenish; often it is concentrically zoned.
HARDNESS 5 - 5.5
SPECIFIC GRAVITY 2.2 - 2.4
LUSTER Vitreous to sub pearly
STREAK White
BREAKABILITY Brittle, has one very good cleavage and one good cleavage; uneven to splintery fracture.
OCCURRENCE Thomsonite is most often found as a filling of a fracture or void in mafic igneous rocks like basalt.
ASSOCIATED MINERALS Other Zeolites, Calcite, Datolite, Quartz
MINERAL NAME Named for Thomas Thomson, the Scottish chemist who first analyzed the mineral.