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Chemical composition Ca2(Mg,Al)6(Si,Al,B)6O20
Crystal system Triclinic
Habit Tabular/Granular
Cleavage None
Fracture Sub-concoidal, uneven
Hardness 6-7
Optic nature Biaxial (+) or (-)
Refractive index 1.701-1.706
Birefringence .005
Specific gravity 3.42-3.52
Lustre Vitreous
Pleochroism Strong

X: pale yellow, yellow-green to blue-green
Y: almost colorless, pale yellow, blue-green, blue
Z: pale blue to dark blue