Sapphire is a gemstone  variety of the mineral corundum, an aluminium oxide (α-Al2O3), when it is a color other than red, in which case the gem would instead be a ruby. Trace amounts of other elements such as iron, titanium, or chromium  can give corundum blue, yellow, pink, purple, orange, or greenish color. Pink-orange sapphires are also called padparadscha.

Because it is a gemstone, sapphire is commonly worn as jewelry. Sapphire can be found naturally, or manufactured in large crystal boules. Because of its remarkable hardness, sapphire is used in many applications, including infrared optical components, watch crystals, high-durability windows, and wafers for the deposition of thin films of various semiconductors.

Natural Sapphires

Sapphire is one of the two gem varieties of corundum, the other being the red ruby. Although blue is the most well known hue, sapphire is any color of corundum except red. Sapphire may also be colorless, and it also occurs in shades of gray and black.

The cost of natural sapphire varies depending on their color, clarity, size, cut, and overall quality as well as geographic origin. Significant sapphire deposits are found in Eastern Australia, Thailand, Sri Lanka, Madagascar, East Africa and in the United States at various locations (Gem Mountain) and in the Missouri River near Helena, Montana. Sapphire and rubies are often found together in the same area, but one gem is usually more abundant.

Synthetic sapphire

In 1902, French chemist Auguste Verneuil developed a process for growing synthetic sapphire crystals. In the Verneuil process, fine alumina powder is added to an oxyhydrogen flame which is directed downward against a mantle. Alumina in the flame is slowly deposited, creating a teardrop shaped 'boule' of sapphire. Chemical dopants can be added to create artificial versions of ruby and all the other sapphire gems, plus colors never seen in nature. Artificial sapphire is identical to natural sapphire, except it can be made without the flaws found in natural stones. The disadvantage of Verneuil process is the grown crystals have high internal strains. Many methods of manufacturing sapphire today are variations of the Czochralski process invented in 1916. A tiny sapphire seed crystal is dipped into a crucible of molten alumina and slowly withdrawn upward at a rate of 1 to 100 mm per hour. The alumina crystallizes on the end, creating long carrot shaped boules of large size, up to 400 mm in diameter and weighing almost 500 kg.

The first laser was made with a rod of synthetic ruby. Titanium-sapphire lasers are popular due to the relatively rare ability to tune the laser wavelength in the red-to near infrared region of the electromagnetic spectrum. They can also be easily mode-locked. 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.

Source : Wikipedia