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Colorless sapphire
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 leykds, 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 Sri Lanka. 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 retractive. 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 Sri Lanka, where quantities of light-colored
corundum are found, but is apparently also found in Burma
and elsewhere. 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. I? has been produced synthetically and as with the
other pale varieties, the internal features characteristic
of Verneui synthetic corundum are very well disguised. Synthetic
leucosapphire is used mainly as a diamond simulant, particularly
for small stones, in which the differences are lessapparent.
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