A cubic zirconia is a real cubic zirconia, but it is not a real diamond. However, there are a few types of stones that are used as diamond simulants, and cubic zirconia is by far the most common and the most realistic. In fact, Simon G. engagement rings feature cubic zirconia center stones.

Additionally, cubic zirconia lacks the brilliance and fire that a diamond has, meaning light passes through it differently than it would through a diamond. Cubic zirconia also has a higher dispersion rate, which is why it often gives off that rainbow effect that can make it look cheaper.