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