Riesling

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Riesling beryl
Chemical composition Be3Al2(SiO3)6 Beryllium aluminum silicate
Crystal system Hexagonal
Habit Prismatic
Cleavage Poor, basal
Fracture Conchoidal to uneven
Hardness 7.5
Optic nature Uniaxial -
Refractive index 1.59
Birefringence 0.004 - 0.009
Dispersion Low, 0.014
Specific gravity 2.66 -2.86
Lustre Vitreous
Pleochroism Strong