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Sapphire is a gem-variety of the mineral corundum, colored in blue with light purple or green hues or without them in Russia. The Russian name comes from the ancient Greek "Σάπφειρος" - a stone of blue color. Blue sapphires are graded basing upon the purity of their primary hue – blue sapphire in world practice.

Chemistry: Al2O3;

Crystal system: Trigonal, ditrigonal-skalenohedral crystal class (point symmetry group);

Color: Blue, blue with a purple hue, blue with a faint green hue.

The blue color is due to trace amounts of elements such as Fe2+ – Ti4+ in the lattice of the mineral.

Identification properties

Physical properties
Mohs hardness: 9
Density: 4.00±0.03 g/cm3
Cleavage: none
Fracture: conchoidal
Optical properties
Optical character: anisotropic, uniaxial, negative
Refractive Index:

ne = 1.760-1.764,

no = 1.768-1.772

Birefringence: 0.008 – 0.009
Pleochroism: from weak to distinct in violet, yellow, green tones
Dispertion: 0.018 (BG)
Luster: vitreous

Inclusions and structural inhomogeneities