apophyllite

noun

apo·​phyl·​lite ˌa-pə-ˈfi-ˌlīt  ə-ˈpä-fə-ˌlīt 

: a mineral composed of a hydrous silicate of potassium, calcium, and fluorine that is related to the zeolites and is usually found in transparent square prisms or white or grayish masses

Word History

Etymology

French, from apo- + Greek phyllon leaf — more at blade

First Known Use

circa 1807, in the meaning defined above