Stone Story
A lab-grown diamond has the same carbon crystal structure, Mohs hardness of 10, and refractive index as a natural diamond. Cubic zirconia is zirconium oxide: denser, softer at 8 to 8.5 on the Mohs scale, and with a different refractive profile. In a set stone, the two look similar. In a gemological test, they are immediately distinguishable.