What Is the Way to Tell the Difference Between a Cubic Zirconia and a Real Diamond?

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The best way to tell if a stone is a real diamond or a cubic zirconia is by using a pen-sized probe called a diamond tester. When looking at the surface of the stone, a real diamond will be free from scratches and the diamond will refract a gray light.

Another way to test a stone to see if it is a real diamond is to try to scratch glass with it. A real diamond is hard enough to put a scratch in a piece of glass, but a cubic zirconia will do nothing. With enough pressure, the CZ gem could actually break under pressure.