Apophyllite Group - (K,Na)Ca₄Si₈O₂₀(OH,F)·8H₂O

Habit: Colorless, white, pink, yellow or green. Crystals tabular to prismatic, commonly pseudo-cubic, with prism zone deeply striated; also granular. Vitreous to pearly luster; transparent to translucent. White streak.

Environment: A product of low-grade regional and contact metamorphism and a late-stage hydrothermal mineral in some mineral deposits. Also a secondary mineral in amygdules or druses in basalts and in cavities in granite.

Etymology: From the Greek words for "away from" and "leaf," in allusion to its manner of exfoliating on heating.

Colorless and green apophyllite-group minerals from India are popular with collectors and are even faceted into gemstones. Apophyllite-group minerals are found in ancient lava and basalt flows. Cavities or other open spaces in the rock allow these blocky crystals to grow unimpeded. Apophyllite-group minerals are also found in voids in limestones, in the contact metamorphic zone that surrounds the intrusive rocks.