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Chemical composition Complex calcium aluminum silicate
Crystal system Tetragonal
Habit Prismatic terminated by truncated pyramids, massive, fibrous
Cleavage Poor
Fracture Sub-conchoidal
Hardness 6.5
Optic nature Uniaxial +/-
Refractive index 1.700 - 1.725
Birefringence 0.005
Dispersion Low, 0.019
Specific gravity 3.25-3.50
Lustre Vitreous
Pleochroism Weak to distinct (shades of body color)