There are two very different causes of yellow coloration in sapphires. The presence of iron as a trace element in corundum produces green and yellow sapphires, and when mixed with titanium, produces blue sapphires.Ī radiant cut yellow sapphire finds its color from traces of iron. Blue sapphires also need trace amounts of the following element, iron. Too much color saturation can create a dull or overly dark effect in the blue sapphire, which is not desirable and lowers the price of the stone. The higher concentrations of titanium in the sapphire, the more color saturation. The blue color in a blue sapphire comes from the mineral titanium that is within the crystal. TitaniumĪ stunning royal blue Kashmir sapphire that gets its color from the presence of titanium. It is only with the additional of trace elements that corundum gains its rainbow of hues. In it’s purest form, corundum is colorless and clear, resulting in white sapphires. As silicon is a very common element in the earth’s crust, natural corundum is relatively rare to find. It requires an environment free of silicon in order to grow. Crystalline minerals are classified by seven different crystal systems that are separated depending on the symmetry of their repeated atomic units.Ī piece of Sri Lankan padparadscha rough crystal.Ĭorundum has a trigonal crystal structure and is composed only of aluminum and oxygen. Corundum has a regular crystalline structure formed by repeating patterns of arrangement at the atomic level. Sapphires and rubies are corundum, which is an aluminum oxide (Al2O3.).
In essence, rubies are red sapphires because they belong to the same corundum species, just a different variety. As a variety of corundum, sapphires come in all colors, except red. Rough blue sapphire crystal in cornflower blue.ĭifferent varieties of corundum are distinguished by characteristics of color, transparency, internal features, and optical phenomena. Old lawn chairs may be coated with a thin layer of corundum if their aluminum surfaces have oxidized. “Emery” is a common variety of corundum that is used as a commercial abrasive. Many of these varieties are not as rare or valuable as sapphire. Corundum (a mineral species) comes in a number of different varieties. How Are Sapphires Categorized?Ī “variety” is a subgroup of a mineral species. In gemology, a “species” is a mineral that has a definite chemical formula and a specific three-dimensional structure. Sapphires, and their close cousins, rubies, are members of the corundum mineral species. Cornflower blue Kashmir sapphire crystal rough.
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