Dioptase

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Dioptase
Chemical composition CuSiO3H2O
Crystal system Trigonal
Habit Prismatic
Cleavage Perfect, rhombohedral
Fracture Conchoidal to uneven
Hardness 5
Optic nature Uniaxial +
Refractive index 1.644 - 1.709
Birefringence 0.053
Dispersion Medium, 0.030
Specific gravity 3.28 - 3.35
Lustre Vitreous
Pleochroism Weak
Faceted Dioptase
Photo courtesty of The Gem Trader