Lab-grown diamonds and cubic zirconia are both popular alternatives to natural diamonds. They are both beautiful, durable, and affordable. However, there are some key differences between the two stones.Cubic zirconia is a different mineral than diamond. It is made up of silicon carbide, while diamonds are made up of carbon. Cubic zirconia is slightly less hard than diamond, but it is still very durable. Cubic zirconia also has a higher refractive index than diamond, which means that it sparkles more.