When the crystal structure of corundum does not contain trace elements that act as colorants, it is completely clear, although this form is the least known and appreciated on the gem market. The name of leucosapphire, coined fairly recently, is derived from the Greek leykos, meaning “white.”
Appearance It is perfectly colorless or occasionally has a slight yellow tinge and has the typical luster of corundum It can have fine veillike and lacelike liquid inclusions and even areas that look cloudy in bright light, due to the presence of fine, crossed needles or minute straws of rutile; it may also have small crystalline inclusions with minute cracks radiating from them, like much corundum from SriLanka. It is given a round (or almost round) mixed cut, or a slightly modified brilliant cut, having mainly been used as a substitute for diamond.
Distinctive features Despite its luster, it is very easily distinguished from diamond, which it was once meant to simulate. It has less dispersion and fire, plus weak birefringence, where visible. Diamond, of course, is singly refractive. The faint yellow coloration of some colorless sapphires can, however, make them more plausible as imitations. Colorless corundum is distinguished from colorless zircon by the pronounced birefringence of the latter.
Occurrence Colorless sapphire comes mainly from Lank , where quantities of light-colored corundum are found, but is apparently also found in Burma and else where. It is of little interest as a gemstone and is chiefly used for industrial purposes as an abrasive.
Value Very low, but hard to quantify, as it now has scarcity value for collectors and amateurs.
Stimulants and synthetics Colorless corundum has not been imitated, but was formerly used to imitate diamond. lt has been produced synthetically and as with the other pale varieties, the internal features characteristic of Verneuil synthetic corundum are very well disguised. Synthetic leucosapphire is used mainly as a diamond simulant, particularly for small stones, in which the differences are less apparent.