Template:Tourmaline

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Tourmaline
Chemical composition Complex borosilicate
Crystal system Trigonal
Habit Trigonal prisms with convex faces
Fracture Concoidal
Hardness 7.5
Optic nature Uniaxial -
Refractive index 1.62 - 1.64
Birefringence 0.014-0.021 (up to 0.039)
Dispersion Low, 0.018
Specific gravity 3.06 (3.01-3.11)
Lustre Vitreous
Pleochroism Weak to strong