Apophyllite
Apophyllite ({not transcribed}) , noun
[Prefix apo- + Greek {not transcribed} leaf; so called from its foliated structure or easy cleavage.]
(Mineralogy) A mineral relating to the zeolites, usually occurring in square prisms or octahedrons with pearly luster on the cleavage surface. It is a hydrous silicate of calcium and potassium.