Sapphires
Sapphire is the official birthstone for the month of September as adopted by the American National Association of Jewelers in 1912. It is also one of the birth stones for the Zodiac signs of Pisces, Taurus, Virgo and Sagittarius. Sapphire is given as a gem for the 5th, 23rd and 45th wedding anniversaries while a star sapphire is given on the 65th wedding anniversary.
Sapphire is the non-red variety of corundum. The red variety of corundum is ruby. A 9.0 on the Mohs scale of hardness, sapphire is the second hardest natural mineral.
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 what creates the illusion of a star in Star Sapphire.
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.
A rare variety of sapphire, known as color changing sapphire, exhibits different colors in different light. A color change sapphire is blue in natural light, and violet in artificial light. A similar effect is also seen in alexandrite.
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