Trace amounts of iron and titanium can produce a blue color in corundum. Blue corundums are known as “sapphires.” The name “sapphire” is used for corundums that range from a very light blue to a very dark blue color. The blue can range from a greenish blue to violetish blue. Gems with a rich blue to violetish blue color are the most desirable.

Gem-quality corundum occurs in a wide range of other colors, including pink, purple, orange, yellow, and green. These gems are known as “fancy sapphires.” It is surprising that a single mineral can produce gemstones of so many different colors.

When the color of a sapphire is any color other than blue, the color should be used as a preceding adjective to describe the stone. For example, pink sapphire, yellow sapphire, or green sapphire. Used alone, the word “sapphire” refers only to blue corundum.