Blue Sapphire

Sapphire is the most precious and valuable blue gemstone. It is a very desirable gemstone due to its excellent color, hardness, durability, and luster. Gemstone color can be described in terms of hue, saturation, and tone. Hue is commonly understood as the “color” of the gemstone. Saturation refers to the vividness or brightness of the hue, and tone is the lightness to darkness of the hue. Blue sapphire exists in various mixtures of its primary (blue) and secondary hues, various tonal levels (shades) and at various levels of saturation (vividness).
Color has the most important influence on blue sapphire’s value. The most highly valued blue sapphires are velvety blue to violetish blue, in medium to medium dark tones. Preferred sapphires also have strong to vivid color saturation. The saturation should be as strong as possible without darkening the color and compromising brightness. Sapphires with these qualities command the highest prices per carat.

Ceylon Blue Sapphire

Blue corundum in all shades are identified as sapphires. Sri Lanka sapphires are universally renowned for their magnificent quality and the large sizes in which these sometimes occur. Every possible shade of blue is represented among sapphires of Sri Lanka, the various shades ranging from the palest to the darkest. Flawless, transparent sapphires of a deep blue colour are highly prized. High quality blue sapphires from Sri Lanka are reputed for having a pleasing tone of colour, whatever the shade and are of remarkable transparency. In superior quality material the degree of transparency is very high and its clarity is excellent. These features in combination could produce a very high Iustre which in turn imparts a sparkle to the gemstone. Although the distribution of colour in sapphire is characteristically patchy, an apparent colour evenness is seen because of its highly transparent body. Sapphires of over ten carats with all the above features combined are not uncommon in Sri Lanka. Comparatively, stones with such combination of characteristics are rarely seen in other localities. The smaller commercial grades are more abundant.

Category Oxide mineral
Composition 

Formula

Aluminium oxide, Al2O3
Crystal system Trigonal
Crystal class Hexagonal scalenohedral (3m)
H-M symbol: (32/m)
Space group R3c
Identification
Color Typically blue, but varies
Crystal habit As crystals, massive and granular
Fracture Conchoidal, splintery
Mohs scalehardness 9.0
Luster Vitreous
Specific gravity 3.95–4.03
Optical properties Abbe number 72.2
Refractive index nω=1.768–1.772
nε=1.760–1.763,
Birefringence 0.008
Pleochroism Strong
Melting point 2,030–2,050 °C
Fusibility Infusible
Solubility Insoluble
Other characteristics Coefficient of thermal expansion (5.0–6.6)×10−6/K

relative permittivity at 20 °C
ε = 8.9–11.1 (anisotropic)[1]

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