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September Birthstone - Sapphire
Physical and Chemical Properties
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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