Prehnite | Botryoidal green crystal, mineral specimen from MaliPrehnite from Mali is prized for its soft, luminous green hues and naturally sculptural crystal forms. Typically forming as botryoidal, globular, or stalactitic aggregates, Malian prehnite often shows a delicate translucency that gives it a gentle, glowing depth. Geologically, prehnite is a calcium aluminum silicate that crystallizes in low grade metamorphic and hydrothermal environments, and Malis material is especially admired for its clean surfaces