Apophyllite \A*poph"yl*lite\, n. [Pref. apo- + Gr. ? leaf; so
called from its foliated structure or easy cleavage.] (Min.)
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.
[1913 Webster]