Zoisite - Ca₂Al₃(SiO₄)(Si₂O₇)O(OH)

Habit: Yellowish green, green, brown, blue (tanzanite); colorless, purple, gray or pink (thulite). Crystals prismatic, vertically striated. Vitreous luster, sometimes pearly on cleavage; transparent to translucent. White streak.

Environment: Occurs in regional and contact metamorphic rocks; also in quartz veins, pegmatites and some eclogites.

Etymology: Named for Siegmund Zois, Baron von Edelstein (1747-1819), an Austrian natural scientist.