Noun

1. A mineral found in crystalline schists, a metamorphic product of calcium feldspar.
   • Composition: Hydrous calcium aluminum silicate $Ca\_2Al\_3O\; (SiO\_4)\; (Si\_2O\_7)\; (OH)$
   • Habit: Prismatic crystals with striations parallel to the b-axis.
   • Physical characteristics: Hardness 6-6.5; Specific gravity 3.25-3.37; Luster vitreous, transparent to translucent; Color gray to green or pink.