Cubic Zirconia (8.07)
Cubic zirconia, commonly called CZ, is the most successful diamond imitation in history due to its high refractive index and cheap cost. CZ will be very easy to distinguish from diamond since their properties are generally contrasting.
If you cannot identify a CZ at first glance, then an easy method of identification is its specific gravity. This will only apply to a loose stone, since it will have to be weighed. With an average specific gravity of 5.5 to 6, a CZ is 56% to 70% heavier than a similar diamond -- which should make it very obvious when you place it on a scale. If the diameter of the normally proportioned stone is 6.4 mm and it weighs 1.60 carats, you can be assured that it is not a diamond and very likely a CZ.
Other obvious non-diamond features include: Polishing lines all lying in the same direction, the absence of natural diamond inclusions, and obviously rounded facet edges. CZ is singly refractive so the doubling effect detection method cannot be used.
The hardness of CZ varies, depending on the manufacturer, but it is generally on the softer side since it is easily scratched. A company called Asha is introducing a CZ that is coated with a diamond-like carbon substance for a harder surface. Generally the facet edges are rounded to reduce edge wear and nicks. The fracture type is conchoidal, which is manifested in a CZ as a smooth shell-like chip. CZs that have been worn in a ring for some period of time, will generally be at least slightly damaged due to their soft nature.
Look for obvious wear on the crown, which could include abrasions, scratches, chips, and nicks.