Stilbite Group - NaCa₄(Si₂₇Al₉)O₇₂·28H₂O; Na₉(Si₂₇Al₉)O₇₂·28H₂O

Habit: White, yellowish, gray, pink, reddish, orange or light to dark brown. Crystals thin tabular, sheaf-like or in globular clusters. Vitreous luster, but pearly on cleavage; transparent to translucent. White streak.

Environment: A low-temperature hydrothermal mineral found in amygdules and cavities in basalt.

Etymology: From the Greek word for "luster," in reference to its pearly luster. The stilbite group is made up of two minerals, stilbite-Ca and stilbite-Na.