Source : Webster's Revised Unabridged Dictionary (1913)

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.