Emerald, along with other beryls, is quite hard, having a hardness of 71/2 to 8 on Moh's scale, compared with 10 for diamond, 9 for corundum, and 8 for topaz. Hardness is generally a desirable feature is gemstones.
Chemical Composition and Name Be3Al2(SiO3)6 - Beryllium Aluminium Silicate
Hardness 7.5 to 8
Refractive Index 1.560 - 1.565 to 1.587 to 1.593
Specific Gravity 2.65 to 2.76
Birefringence 0.005 to 0.009
Crystalline System Hexagonal
Optic Sign Negative
Other Optical Properties Uniaxial
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