Cubic zirconia is perhaps the most common type of fake diamond. Cubic zirconia is the cubic crystalline form of zirconium dioxide. It is extremely inexpensive, durable, and looks very similar to actual diamond, which make it the most popular choice for fake diamond. Cubic zirconia is usually flawless and colorless, which means that not only is it very similar to diamond, but it is very similar to high quality diamond.
On the Mohs hardness scale, cubic zirconia has a rating of between 8.5 and 9. Diamond has a rating of 10 (the highest rating possible). So CZ is almost as hard as diamond, but it can still be scratched, although most materials will not be able to hurt it, as most things are softer than CZ. For example, a steel file has a hardness rating of around 6.5 and therefore would not be able to scratch CZ.
Cubic zirconia is heavier than diamond. For a diamond and CZ that are the same size, the CZ will weigh about 1.7 times more. This has no effect on its function as jewelery, however, because the sizes used for gemstones are small enough that any difference in weight is negligible.
Cubic zirconia can be made to be colorless. With diamonds, it is extremely rare (and expensive) to have a completely colorless stone (which would be a color rating of “D” on the diamond color scale). So CZ not only imitates diamond, but it imitates the highest quality of diamond.
The dispersion of CZ is 0.060, whereas diamond is 0.044, which means that CZ will have more “fire” than a diamond.
As CZ is a bit softer than diamond, if you are mounting a CZ stone into a setting meant for a diamond, make sure you tell the jeweler so the CZ doesn’t get damaged. The procedure for mounting a CZ is slightly different from mounting a diamond.