Star sapphire is a member of the corundum family. Red corundum is called ruby, all other color varieties of corundum being referred to as sapphire. Corundum is the second hardest substance on the Mohs scale, with a rating of 9. Diamond tops that scale with a ten. Star sapphires contain unusual tiny needle-like inclusions of rutile. Aligned needles that intersect each other at varying angles produce a phenomenon called asterism. Star sapphire range in color from blue in various tones, to pink, orange, yellow, green, lavender, gray to black. The most desirable color is a vivid, intense blue. Star sapphire is a durable, popular stone for men's rings. In ancient times, star sapphire was regarded as a powerful talisman guiding travelers and seekers of all kinds. Star sapphire range in color from blue in various tones, to pink, orange, yellow, green, lavender and gray to black. The coloring agents in blue sapphire are iron and titanium and, in violet stones, vanadium. A small iron content only results in yellow and green tones, chromium produces pink, iron and vanadium orange tones. The most desirable color is a vivid, intense blue. The six-rayed-star light effect appears most clearly under natural light. Included rutile needles cause the star effect. Less transparent sapphires, translucent or opaque stones, are cut en cabochon to support the star effect with its six rays. The best cabochons are somewhat transparent, with smooth domes of good symmetry. One should look for an even roundness to the shape.
The most important deposits today are in Australia, Myanmar, Sri Lanka and Thailand. Other significant star deposits are in Brazil, Cambodia, China, Kenya, Madagascar. Malawi, Nigeria, Pakistan, Rwanda, Tanzania, United States (Montana), Vietnam and Zimbabwe.
The most common treatment for star sapphire is heat treatment. Stones, generally before they are cut, are heated to between 1700 to 1800 degrees Celsius (3100-3300 degrees F) for several hours. Heating often improves the color and clarity of the gem. A reputable dealer will always disclose if stone has been subject to heat treatment. Diffusion treatment is sometimes used to improve the star effect in star sapphire. The sapphire is heated with titanium to create a more distinct star.
The Smithsonian Institution in Washington D.C. displays a star sapphire of more than fifty carats that was found in Sri Lanka. The mega-star of its impressive gem collection is the "Star of Asia", a star sapphire of 330 carats. Actress Mary Pickford loved very large rubies and star sapphires. She owned both the 60-carat Star of Bombay and the 200-carat Star of India, and often wore them both at the same time.
Star sapphire Gemology
Color: Blue in various tones, pink, yellow, green, lavender, gray, black
Chemical composition: Al2O3 aluminum oxide
Crystal system: (Trigonal) doubly pointy, barrel-shaped, hexagonal pyramids, tabloid-shaped
Hardness: 9 (Mohs scale)
Specific gravity: 3.95 - 4.03
Refractive index: 1.762 -1.778
Absorption spectrum: Blue s. 471, 460, 455, 450, 379; yellow 471, 460, 450, brown 471, 460-450
Fluorescence: Blue none; colorless orange-yellow, violet
Sapphire is the birthstone for those who are born in September. On the Zodiac chart, it is regarded as the stone for Taurus.
The ancients regarded star sapphires as a powerful talisman protecting travelers and seekers. They were considered to be so powerful, they would continue protecting the wearer even after being passed on to another person.
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