Specific gravity - CZ weighs more than diamonds. A CZ will weigh an average of 1.7 times more than a diamond of the same size.
Refractive index - CZ has a refractive index of 2.176 compared to 2.417 for diamond.
Thermal conductivity - CZ is a thermal insulator, while diamonds are thermal conductors.
The more detailed methods(About JEWELRY)
1.Take your jewelry to a professional jeweler for a definitive answer. A jeweler has special magnifying glasses and lights that he can use to look at the gem. Some cubic zirconia stones are of such high quality that even a professional cannot make a definite conclusion without special tools.
2.Compare the weight of a cubic zirconia stone to a diamond. CZ stones are heavier than diamonds, making it necessary to measure them in millimeters, measuring the diameter, instead of carats, which is a unit of weight. Some jewelers estimate that CZ stones weigh almost twice what genuine diamonds weigh, and others claim that a cubic zirconia weighs about 75 percent more than a diamond of equal size.
3.Try the fog test to tell the difference between a cubic zirconia and a diamond. If you breathe on a diamond in the same way you would breathe on a mirror, it would stay clear without fogging at all. Do the same to a CZ and it will fog up. This is because a diamond will not retain heat and a CZ will.
4.Look at the color of the gem. Compared to diamonds, CZ stones have a rainbow of colors emanating from the stones, whereas diamonds sparkle a white color. CZ stones generally sparkle less brilliantly than a genuine diamond.
5.Watch for chips and scratches. If you have a CZ stone in your jewelry instead of a diamond, expect it to chip and scratch more easily. While a diamond has a hardness rating of 10, a CZ has a hardness rating of 8.5.
6.Find out the price of the jewelry, if possible. If the stone is huge and the price is low, this should tell you that the stone is probably not a genuine diamond. Cubic zirconia stones often have sterling silver mountings instead of 14-carat gold mountings because silver is relatively inexpensive compared to gold. Cubic zirconia jewelry is frequently gold-plated metal as well.
Testing the Difference
To the naked eye, there is virtually no difference between CZ and real diamonds. The only test one might try is to look at two stones and see which outshines or outsparkles the other. With CZ, the shine will be more brilliant than a real diamond because of CZ’s higher rate of dispersion. All other tests to tell the difference require a jeweler’s loupe or microscope. Jewelers will look at the stone under magnification to see if it has any inclusions, or flaws. These will be absent in CZ but are present in almost all diamonds. If you’d really like to know whether your stone is CZ or a real diamond, take it to a professional jeweler. Usually, jewelers do not charge for this service and can make a quick assessment. If he is unsure, he can recommend that you send the stone to a gem lab for accurate identification.
How do you protect cubic zirconia jewelry and prevent them from fading and becoming dull over time?
Loose Cubic Zirconia VS Diamonds