A gem variety of corundum, coloured by the addition of minor amounts of impurity. It occurs in a variety of colours (except red, when it is termed ruby), but blue is the most valuable.
| Sapphire | |
|---|---|
| General | |
| Category | Mineral |
| Chemical formula | aluminium oxide, Al2O3 |
| Identification | |
| Color | Blue, pink, yellow, green, white, and parti-colour |
| Crystal habit | massive and granular |
| Crystal system | Trigonal |
| Cleavage | None |
| Fracture | Conchoidal, splintery |
| Mohs Scale hardness | 9.0 |
| Luster | Vitreous |
| Refractive index | 1.762-1.778 |
| Pleochroism | Strong |
| Streak | White |
| Specific gravity | 3.95-4.03 |
| Fusibility | infusible |
| Solubility | insoluble |
| Major varieties | |
| Ruby | When contaminated with chromium |
| Oriental topaz, amethyst, emerald | Yellow, purple or green sapphires |
Sapphire (from Hebrew: ספּיר Sapir) is the single-crystal form of aluminium oxide (Al2O3), a mineral known as corundum. Trace amounts of other elements such as iron and chromium give sapphires their blue, red, yellow, pink, purple, orange or greenish color. Sapphire includes any gemstone quality varieties of the mineral corundum including the red variety, which is also known as ruby.
Sapphires in nature
Blue sapphires come in a wide range of shades of blue. Pink sapphires are have trace element of chromium and the deeper the color pink the higher the value as long as the color is going toward red of rubies. Color shift sapphires are blue in outdoor light and purple in indoor light.
Synthetic sapphire for non-gemstone applications
Synthetic sapphire crystals can be grown in cylindrical crystal ingots of large size, up to many inches in diameter. As well as gemstone applications there are many other uses:
The first ever laser produced was based on the ruby chromium impurity in sapphire.
Pure sapphire ingots can be sliced into wafers and polished to form transparent crystal slices. Since sapphire ranks a 9 on the Mohs Scale, owners of such watches should still be careful to avoid exposure to diamond jewelry, and should avoid striking their watches against artificial stone and simulated stone surfaces.
Wafers of single crystal sapphire are also used in the semiconductor industry as a substrate for the growth of gallium nitride based devices.
Star Sapphire
A star sapphire is a type of sapphire that exhibits a star-like phenomenon known as asterism.
The value of a Star Sapphire depends not only on the carat weight of the stone but also the body color, visibility, and intensity of the star. Some sapphires are heat-treated or otherwise enhanced to improve their appearance and color, though some people object to such practices and prefer natural untreated stones.
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