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In the gem world, all kinds of gem-quality corundum other than ruby are called sapphire. The mineral name of sapphire is corundum, which belongs to the corundum group of minerals. In fact, the gem-quality corundum in nature is called sapphire, or colored sapphire, except for red called ruby, and other colors such as blue, light blue, green, yellow, gray, colorless, etc. Sapphire is preceded by a color name, such as pink sapphire. The chemical composition of sapphire (Al2O3) is mainly Fe, Ti, and color. Corundum contains iron (Fe) and titanium (Ti) and other trace elements, and presents blue, sky blue, light blue and other colors, among which the royal blue and cornflower colors that are considered to be thick but not black are the best. In cabochon cutting, when the interior is rich in three groups of inclusions parallel to the bottom surface and oriented, it can produce beautiful six-shot starlight, which is called star sapphire
The composition of sapphire is alumina, which is blue due to the trace elements titanium (Ti4) or iron (Fe2). It belongs to the trigonal crystal system, and the crystal form is often cylindrical, short column, plate, etc., and the geometry is mostly granular or dense block. Transparent to translucent, vitreous luster. The refractive index is 1.76-1.77, the birefringence is 0.008, and the dichroism is strong. Heterogeneous body. Sometimes it has a special optical effect - the star effect. The hardness is 9, and the density is 3.95-4.1 g/cm3. No cleavage, fissure development.
Industrial sapphire is a material used in special vehicles as transparent armor, and with the exception of diamonds, sapphire is harder than any other natural material.
Sapphire belongs to the trigonal crystal system and has a hexagonal structure.
The lattice constants are: a=b=4.758A, c=12.991A
Refractive index 1.762-1.770
Birefringence: 0.008- 0.010
Uniaxial crystal negative light, in some cases abnormal biaxial crystal light
Luster: bright glass luster to adamantine luster
Pleochroism: Colored sapphires have dichroism, generally, dark blue/blue, blue/light blue, blue-green, blue-gray, yellow sapphire has golden/yellow, orange/light yellow, light yellow/ Colorless, wait.