Apophyllite definitions

Webster's 1828 Dictionary

APOPH'YLLITE, n. [Gr. from, and a leaf; so called because of its tendency to exfoliate.]
A mineral occurring in laminated masses or in regular prismatic crystals, having a strong and peculiar pearly luster. Its structure is foliated, and when a fragment is forcibly rubbed against a hard body, it separates into thin lamens, like selenite. It exfoliates also before the flame of a lamp. From its peculiar luster, it is sometimes called by the harsh name, ichthyophthalmite, fish-eye stone.

Merriam Webster's

noun Etymology: French, from apo- + Greek phyllon leaf — more at blade Date: 1810 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

Webster's 1913 Dictionary

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.