Corundum (Ruby & Sapphire)
Corundum is an aluminum oxide with a hardness of 9, second only to the diamond. The more valuable varieties of corundum come from Sri Lanka, Thailand, America, Cambodia, Burma, Australia, India, and Tanzania.
A ruby is red corundum. Most rubies contain inclusions, therefore the more valuable rubies contain a small amount of inclusions. A ruby is just a notch below the diamond and emerald as far as value of the cut gem. Most of the very high quality rubies come from Burma.
A sapphire is blue corundum. This color can be a dark blue to almost black. Sapphires polish very well, like all corundums, and have a nice luster. Sapphires are also very valuable and are comparable to the prices of rubies.
All other colors of corundums have a variety of names, such as pink rubies, pink sapphires, violet sapphires, yellow sapphires, green sapphires, and colorless sapphires.
Additional corundums that are rather popular are the star ruby and star sapphire. These stones have a six-ray star visible from almost any angle. Very fine needles of rutile within the corundum cause this star.
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