KAlSi₂O₆ A white or gray rock-forming mineral belonging to the feldspathoid group; at ordinary temperatures the mineral exists as aggregates of trapezohedral crystals with glassy fracture; hardness is 5.5-6.0 on Mohs scale, and specific gravity is 2.45-2.50. Also known as amphigene; grenatite; vesuvian; Vesuvian garnet; white garnet.