Chemical Composition of Sapphires

Sapphires are known for their deep, blue color and romantic history. The gemstone is associated with royalty, and in fact many of these stones can be found in the crowns of European royalty, as well as in the gem collections of ancient Asian potentates. Sapphires get their color from the chemical composition that occurs within the stone when it is formed. Sapphires can vary in color depending on the types of impurities that are present.

How Sapphires Are Created

Sapphires are in the mineral group called corundum. Conumdum includes both rubies and sapphires, though the two types of stones are different in their composition. Corundum is an aluminum oxide compounds that forms in metamorphic rocks such as schist’s and igneous rocks such as senate, nightline senate and pegmatite. Volcanic processes deep within the Earth form aluminum oxide. The high temperatures and pressures cause the liquid magma to form crystals, which become the gemstones that we know. Much of the sapphires that are mined come from stream deposits that have been pushed to the surface over millions of years. 

Chemical Components of Sapphire Stones

Sapphire stones are composed of aluminum oxide, generally AlO3, that is a very hard material formed by geologic processes. It is only second to the diamond in hardness.  Aluminum oxide is clear and colorless in it pure form. Sapphires may also contain small amounts of other minerals like iron or titanium. The amounts of impurities within the stones and the forces of nature that worked on them determine all differences in color. 

Variations in Chemical Composition

The tiny amounts of chemicals within the crystals join together to give the sapphire its color. Sapphires can range in color from pink, orange and green to light or very deep blue shades. These variations are produced by the percentages of iron or titanium in the stone. Colors also occur because of the transfer of electrons between the metal ions. Sapphires are often heated to increase their transparency or color. This process burns off other impurities that may cloud the stone.

The Best Sapphire Stones

Great variations in quality and cost exist in sapphire stones due to the natural conditions under which they are created. Stones with superior clarity and color are the most expensive, while stones with more varied impurities that cause duller color and less transparency, will cost less. Heat-treated stones must be marked as such to inform buyers that they are not in their natural form. Sapphires that are dyed to enhance the color must also be marked as such to prevent confusion.