RhymeZone: laumontite definitions

Definitions of laumontite:

noun: (mineralogy) A mineral, of a white color and vitreous luster, with the chemical formula CaAl₂Si₄O₁₂·4H₂O. It is a hydrous silicate of alumina and lime. Exposed to the air, it loses water, becomes opaque, and crumbles.

(Definitions from Wiktionary)