Tuesday, 19 March 2013

Introduction to Stabilized Cubic Zirconium Oxide

Round brilliant of cubic zirconia.
STABILIZED CUBIC ZIRCONIUM OXIDE 

Cubic zirconium oxide stabilized by the addition of 15 18 percent yttrium oxide (Y203) or 5-8 percent calcium oxide (CaO). It is an artificial product not corresponding to any natural gemstone.

 

Crystal system  


Cubic

Appearance  


Cubic zirconia is produced by the skull melt process and looks like an association of somewhat irregular crystals produced by the cracking of a homogeneous, transparent mass with a light, opaque crust (the wall of the skull It is perfectly transparent and usually perfectly colorless as well but it may be a faint, brownish yellow, due to impurities. It can also be obtained in different colors, such as yellow, violet, red and pink.

Physical properties


It has a hardness of about 8.5 which is good, but less than that of corundum. The density is about 5.65 g x/cm3 or 5.95 g/cm3, depending on the stabilizer used. The refractive index is about 2.17 therefore too high to be measured by ordinary jewelers refract to meters but nonetheless a bit lower than that of diamond

On the other hand, the dispersion 01 0.065 is higher than that of diamond. Production this involves the use of very advanced technology. At present, it is only produced in the United States, Switzerland and the Soviet Union

Djevalite, phianite, cubic zirconia 


These names refer mainly to the colorless variety used as a substitute for diamond. Cubic zirconia looks very similar to diamond and is now much the most widely used diamond stimulant.

Appearance


It is perfectly transparent and colorless highly lustrous and when cut into brilliants or related pear-shaped oval or marquise fancy cuts is extremely similar to diamond while step-cut stones look a bit duller. Its good hardness plus the fact that it is isotropic means that it can be cut with great precision giving sharp facet edges like those obtainable with diamond.

Distinctive

Colorless cubic zirconia, 2.30 ct., set in a ring. Features to the practiced eye, brilliant cut stones show slightly higher dispersion (or fire) than diamond in bright light. Because the refractive index is a bit lower than that of diamond total internal reflection is limited in cut stones thus if they are viewed from above and tilted gradually a dark area will be visible at a certain point through the table facet corresponding to some of the pavilion facets which, instead of reflecting the light, are letting it through. Sometimes the girdle has a distinctive, diagonally striated, transparent appearance unlike that of a diamond, In the case of a loose stone, particularly one of some size 9-10 millimeters in diameter one can feel the density of this material which is almost double that of diamond merely by weighing it in the hand. Cubic zirconia is also hard, but less so than corundum against which it can be tested if need be. This must be done cautiously however. Under a microscope to avoid undue damage to the stone Cost Very low mainly due to the cutting process about the same as that of modern synthetic spinets and corundums.

Writer-Kennie Lyman

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