This is the variety best known to the general public, which for years regarded it as a substitute for diamond capablie of deceiving anyone by its appearance. The name zircon has thus become synonymous with cheap imitation, hopelessly discrediting even the beautiful, colored specimens. less zircon can, apparently, also be obtained by heat treatment of brown or reddish stones. Variations in achieved purely by heating are regarded as normal, not fraudulent, practice.
Appearance Colorless, or with a faint grayish tinge, zircon has outstanding luster, although less than that of the diamond it has normally been required to imitate. If is mainly given a brilliant cut, but often of a slightly different type, with eight extra facets added to the pavilion,starting from the tip, to improve its luster (this is, in fact, known as a zircon cut). Antique stones are often not round, but squarish, with rounded corners, as was once the case with diamonds. Because zircon is somewhat brittle and not very hard, the edges are often slightly damaged. Therefore if is not very suitable for rings, as the stones can easily lose their polish.
Distinctive features Marked birefringence, immediately detectable with a lens from doubling of the facet edges, was and still is the main feature used to distinguish zircon 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 indices are not easily measured, being above the range of most refractometers, but density and hardness can identify it.
Furthermore, most zircons, whatever the color,ususally have a highly characteristic absorption spectrum.
Occurrence Sri Lanka is so renowned for colorless zircons that, in the past, they were known as Matara diamonds (after the city at the southern tip of the island). But Thailand and South Vietnam also have important deposits Value Distinctly low. No longer ih demand as a substitute for diamond, it is of interest mainly to collectors.
Simulants and synthetics It may seem odd that a gem that has chiefly been used to imitate another (Diamond) less synthetic spinel, YAG, and cubic zirconia a pear on the market under the name of zircon. They are obiously imitations, although there can be some confusion over the last because of the similarity of its name. Zircon is not at present produced synthetically.