Sapphires also occur in other natural colors and tints – colorless, gray, yellow, pale pink, orange, green, violet and brown – called fancy sapphires. The most valued shade of blue is the medium-deep cornflower blue. They range from very pale blue to deep indigo, with the exact shade depending on how much titanium and iron lies within the crystal structure.
Typically, sapphires appear as blue stones.
That makes sapphire second in hardness only to diamond. All corundum, including sapphire, has a hardness of 9 on the Mohs scale.
And all other gem-quality forms of corundum are called sapphires. Both are forms of the mineral corundum, a crystalline form of aluminum oxide. September’s birthstone, the sapphire, is a relative of July’s birthstone, the ruby.
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