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Colorless zircon
This is the variety best known to the general
public, whicr for years regarded it as a substitute for diamond
capable c' deceiving anyone by its appearance. The name zircon
har thus become synonymous with cheap imitation, hopelesslv
discrediting even the beautiful, colored specimens. Colorless
zircon can, apparently, also be obtained by heattreatment
of brown or reddish stones. Variations in colo• achieved
purely by heating are regarded as normal, ncfraudulent, practice.
Appearance Colorless, or with a faint grayish
tinge, zircon has outstanding luster, although less than that
of thc diamond it has normally been required to imitate. It
~, mainly given a brilliant cut, but often of a slightly differew
type, with eight extra facets added to the pavilion, startinc
from the tip, to improve its luster (this is, in fact, known
as a: zircon cut). Antique stones are often not round, b~'
squarish, with rounded corners, as was once the case witr
diamonds. Because zircon is somewhat brittle and not ver,
hard, the edges are often slightly damaged. Therefore it not
very suitable for rings, as the stones can easily lose their
polish.
Distinctive features Marked birefringence,
immediatel; detectable with a lens from doubling of the facet
edges was and still is the main feature used to distinguish
zircor from diamond. Examination of the edges which, as mentioned,
in the case of zircon always show signs of brittleness, is
another clue to identification. With regard to the physical
properties of high zircon, the refractive indicee are not
easily measured, being above the range of mos refractometers,
but density and hardness can identify w Furthermore, most
zircons, whatever the color, usuai . have a highly characteristic
absorption spectrum.
Occurrence Sri Lanka is so
renowned for colorless z,, cons that, in the past, they were
known as Matara dimonds (after the city at the southern tip
of the island). B.. Thailand and South Vietnam also have important
depositc Value Distinctly low. No longer in demand as a substitwfor
diamond, it is of interest mainly to collectors.
Simulants and synthetics It may seem odd
that a gethat has chiefly been used to imitate another (diamon=
should in turn be imitated. Yet every now and then colc•less
synthetic spinel, YAG, and cubic zirconia appear c the market
under the name of zircon. They are obvious . imitations, although
there can be some confusion over the last because of the similarity
of its name. Zircon is not w present produced synthetically.
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