September Birthstone - Sapphire

Physical and Chemical Properties

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Chemical composition

Sapphire is a variety of corundum or aluminum oxide and Al203 gives its chemical formula---that is, two parts of Aluminum to three parts of Oxygen. Except for color, all of the other physical and optical properties of sapphire are identical to those of ruby.

Colors

The colors of sapphires and rubies are controlled by trace elements that are included in the crystal lattice in amounts usually not exceeding about three percent. Some of these are:

• Chromium Oxide, Cr203-----ruby
• Titanium Oxide, TiO2 and Ferrous Iron Oxide, Fe203-----blue
• Ferrous Iron Oxide-----yellow
• Chromium Oxide, Ferrous Iron Oxide-----Orange
• Ferric Iron Oxide, Fe304 and Titanium Oxide-----Green
• Chromium Oxide, Ferrous Iron Oxide, Titanium Oxide-----purple

Sapphires can be found in a wide range of colors, such as yellow, green, pink, clear, and most famously, blue; all red corundums are considered rubies. There are many shades possible for blue sapphires, ranging from light clear blue to inky blue-black stones. The most valuable color is called "cornflower" blue. Some sapphires displays streaks of a lighter color that contrast with the darker base.

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