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Chemical composition Complex sodium aluminium silicate
Crystal system Tetragonal
Habit Prismatic and massive
Cleavage Distinct to perfect (depending on direction)
Fracture Conchoidal
Hardness 6
Optic nature Uniaxial -
Refractive index 1.545-1.580 (depending on color)
Birefringence 0.016-0.02
Dispersion Low, 0.017
Specific gravity 2.634-2.74 (depending on color)
Lustre Vitreous
Pleochroism Medium to strong (depending on color)