Euclase - BeAlSiO₄OH

Habit: Colorless, white, pale green to deep yellowish green, greenish blue or pale blue to deep blue. Prismatic crystals and striated, with terminations complex, less commonly flattened. Vitreous luster, somewhat pearly on cleavage faces; transparent to translucent. White streak.

Environment: A product of decomposition of beryl in pegmatites; also occurs in low-temperature alpine veins.

Etymology: From the Greek eu klasis, meaning "good fracture," in allusion to its perfect cleavage.