Sapphire is the non-red variety of corundum (the red variety of corundum is ruby). A 9.0 on the of hardness scale, sapphire is the second hardest natural mineral. Sapphires are formed in igneous and metamorphic rocks. They are a 9 on the hardness scale.

Blue is by far the most popular color for sapphires, but they can be almost any color, including yellow, green, white, colorless, pink, orange, brown, and purple. Padparadscha is the name for a rare orange-pink variety of sapphire and has a higher value than blue sapphires.
Sapphires with inclusions of tiny, rutile needles exhibit an optical property called asterism. This is the star shaped effect seen in star sapphires and is usually only seen in cabochon cuts.

Star sapphires usually have six ray stars, but twelve ray stars are also known. Rarely, when sapphires are cut en cabochon, they can demonstrate a cat's eye effect. This effect displays a thin band of light down the center of the stone and is known as chatoyancy.
 

Heating colorless and very pale blue sapphires to high temperatures is done to give them an intense blue color This treatment can also improve the clarity of the stones by removing tiny inclusions

Sapphires are mined using surface mining like placer mining.

Sapphires are said to have healing properties for colic and rheumatism. It is also believed to aid in the healing of certain mental illnesses. Sapphire is considered an antidepressant as well as an aid to telepathy and clairvoyance.