Cz Versus Diamond

Cubic zirconia is so optically close to diamond that only a trained eye can easily differentiate the two. There are a few key features of CZ which distinguish it from diamond, some observable only under the microscope or loupe. For example: Dispersion. With a dispersive power greater than diamond (0.060 vs. 0.044) the more prismatic fire of CZ can be seen by even an untrained eye. Hardness. CZ has an 8.5 to 9.0 on the Mohs’ hardness scale vs. a rating of 10 for diamonds. http://www.customs-data.com.cn/TALLAGHT-DUBLIN/ Specific gravity. CZs are heavyweights in comparison to diamonds; a CZ will weigh about 1.7 times more than a diamond of equivalent size. Obviously, this difference is only useful when examining loose stones. Flaws. Contemporary production of cubic zirconia is virtually flawless, whereas most diamonds have some sort of defect, be it a feather, included crystal, or perhaps a remnant of an original crystal face (e.g. trigons). Refractive index. CZ has a refractive index of 2.176, compared to a diamond’s 2.417. Cut. Under close inspection with a loupe, the facet shapes of some CZs appear different from diamonds. In theory, many gems (such as CZs and diamonds) look best when the star facet, crown main facets, and upper girdle facets do not quite meet. (Per Step 11 of editor’s note 36 to Marcel Tolkowsky’s Diamond Design.) Diamond has such a high refractive index that having these facets meet at a single point does not cause much loss of fire or reflection. Diamonds normally have these facets meet at a point, because that is more symmetrical and reflects well on the cutter’s precision. On the other hand, CZ has a considerably lower refractive index than diamond. CZs are often cut with 6-sided crown main facets, so that the star facets do not touch the upper girdle facets. This optimizes the brilliance and fire of the CZs. The optimum angle of the main crown facets is steeper for diamond than for CZ. (According to Tolkowsky’s model of the crown, for a given pavilion angle and girdle thickness). CZs are often cut so that the crown main facets do not touch the girdle. This allows the CZs to have a shallower crown angle, while still having the same crown height as a diamond with a similar cut. http://www.customs-data.com.cn/PORT-KAISER/