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TITLE: Rubies and Sapphires

[Photo: Rubies and Sapphires]

Prized for their beautiful colors, rubies and sapphires are both gem varieties of the mineral corundum (aluminum oxide)—the second hardest mineral after diamond. Colorless in its pure state, corundum rarely has sufficient clarity or richness of color to be a gemstone. When it does, the difference between a ruby and a sapphire is just a tiny bit of impurity. Rubies are, by definition, red. The color results from light interacting with a few atoms of chromium trapped as the crystals grew. Ruby is the July birthstone. Sapphires are corundum crystals in all colors but red. Best known are the blue varieties, tinted by iron and titanium impurities. Sapphire is the September birthstone.

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