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Geosciences LibreTexts

16.14.02: Achroite

  • Page ID
    4343
  • 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

    Figure \(\PageIndex{1}\): Achroite Crystal, Pakistan

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