Sapphire a gemstone-quality corundum

Sapphire is any gemstone-quality corundum that is not red. (The red variety of corundum is also known as ruby.)
When color is not specified, sapphire refers to the blue variety. Pink, yellow, green, white, and parti-colour (multi-coloured) sapphires are often valued less than the blue variety of the same quality and size. However a pink-orange sapphire, called a padparadsha, is highly prized. They were found in many countries especially in Asia such as India, Sri Lanka, Thailand, Myanmar, and Cambodia.

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It is the impurities in the aluminium oxide crystal that give the color variations, with different impurity chemical elements giving the different colors that can be found. Pure sapphire is transparent. Traces of iron and titanium give sapphires a blue color. The crystals are exceptionally hard, with only diamond being harder among natural gems. They have a hardness of 9 on the Mohs hardness scale (Diamond is 10).
Gem quality sapphires and rubies occur naturally and can be easily and cheaply produced in the laboratory by the Verneuil process. The chemical compositions and physical properties are identical to the natural sapphires. The tell-tale sign of synthetic sapphires is the crystalline growth lines which are usually curved due to the pulling during the accelerated crystal growth process.

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A version which shows an asterism is called a Star sapphire (see picture above). Although natural sapphires can show an asterism, the shape of the star is usually somewhat irregular and sometimes indistinct. A manufactured star sapphire called the Linde Star shows a very regularly-shaped and distinct asterism because the formation process is more tightly controlled than it is in nature.

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The Logan sapphire is one of the largest blue sapphire gems known. It weighs 423 carats (84.6 g).
Lady Diana Spencer's engagement ring from Charles, Prince of Wales was a sapphire ring.
Cornflower blue is one of the most popular colors for sapphires (the other choice color a deep royal blue), though there is little objective consensus about which shade of blue is the most desirable.
Sapphire is the birthstone associated with September.
The word sapphire is probably Phoenician in origin, coming to English from the Ancient Greek word σάπφειρος, through the Latin sapphirus. It refers to a "blue gem," either the sapphire proper or possibly lapis lazuli.
The major deposits are: Sri Lanka, Thailand, Burma, Cambodia, Nigeria, Madagascar, Australia and Kashmir.

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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. While this laser has few commercial applications, the Ti-sapphire laser is popular due to the relatively rare ability to tune the laser wavelength in the red-to-near infrared region of the electromagnetic spectrum. It can also be easily modelocked. In these lasers, a synthetically produced sapphire crystal with chromium or titanium impurities is irradiated with intense light from a special lamp, or another laser, to create stimulated emission.
Pure sapphire ingots can be sliced into wafers and polished to form transparent crystal slices. Such slices are used as watch faces in high quality watches, as the material's exceptional hardness makes the face almost impossible to scratch. 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. Such surfaces often contain materials including silicon carbide, which, like diamond, are harder than sapphire and thus capable of causing scratches).
Wafers of single crystal sapphire are also used in the semiconductor industry as a substrate for the growth of gallium nitride based blue and green light emitting diodes.
According to Rebbenu Bachya, the word "Sapir" in the verse Exodus 28:20 means "Sapphire" and was the stone on the Ephod representing the tribe of Issachar.

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