Emerald - The Gemology Project
Emerald Chemical composition Be3Al2(SiO3)6 Beryllium aluminum silicate Crystal system Hexagonal Habit Prismatic Cleavage Imperfect, basal Fracture Conchoidal to uneven Hardness 7.5 (brittle) Optic nature Uniaxial - Refractive index 1.566 - 1.600 Birefringe
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