Blue sapphires are the blue variety of the mineral corundum which is crystalline aluminum oxide in which the blue color is caused by the displacement of some aluminum atoms by atoms of titanium and iron. Sri Lankan blue sapphires can vary from delicate sky-blue colors to rich saturated hues. The Sri Lankan sapphire is lighter and brighter than the Kashmir and Burmese sapphires. The Sri Lankan sapphires are a saturated medium blue and does not normally need color enhancement by heating, and usually sold as natural untreated stones. This explains the demand for Sri Lankan blue sapphires, that have received a worldwide branding as premium quality natural blue sapphires, still known in the world gem and jewelry trade as “Ceylon sapphires.”
Some areas of Sri Lanka also produce the famous corn-flower blue sapphires so characteristic of the famous and elusive Kashmir blue sapphires. These sapphires have the unique velvety blue color of the Kashmir sapphires. One area that produced these high-quality sapphires was Rakwana, in the traditional gem producing district of Sri Lanka known as Ratnapura. The Rakwana blue sapphires are the exact look alike of Kashmir blue sapphires, that even several recognized gem testing laboratories in the west originally issued reports certifying them as Kashmir sapphires.
Most Sri Lankan sapphires show an orange-red fluorescence when exposed to long wave length ultra-violet light. Sapphires from other regions of the world are generally inert to ultra-violet light. Thus, the presence of fluorescence in a blue sapphire in ultra-violet light may indicate that the sapphire is of Sri Lankan origin.
One of the commonest solid inclusions found in Sri Lankan sapphires is Zircon. The grains of Zircon are rounded and form haloes known as Zircon haloes. Other inclusions in sapphires include rutile, apatite and spinel.