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Achroite Tourmaline
Chemical composition Complex borosilicate
Crystal system Trigonal
Habit Prismatic
Cleavage None
Fracture Conchoidal
Hardness 7- 7.5
Optic nature Uniaxial -
Refractive index 1.62 - 1.64
Birefringence 0.014 - 0.040
Dispersion Low, 0.017
Specific gravity 3.01 - 3.11
Lustre Vitreous
Pleochroism Strong

NaLi2.5 Al6.5 (BO3)3O18(OH)4

Achroite Crystal: Pakistan

Achroite is a the colorless variety of tourmaline which is usually (but not always) elbaite.