Prehnite - Ca₂Al(Si₃Al)O₁₀(OH)₂

Habit: Light to dark green, white, yellow, gray or pink. Tabular or prismatic to steep pyramidal crystals uncommon; aggregates fanlike, reniform, globular or stalactitic; also granular or compact. Vitreous luster; semitransparent to translucent. Colorless streak.

Environment: A secondary or hydrothermal mineral in veins and cavities in mafic volcanic rocks; a typical product of low-grade metamorphism.

Etymology: Named for Hendrik von Prehn (1733-85), a Dutch colonel who discovered the mineral.

The rough natural state of prehnite hides its potential for beauty. The polishing process brings out a distinctive pearly luster, and its transparent nature gives this stone an almost luminous quality. Individual transparent, gem-quality crystals of prehnite are rare, and they are usually small.