Cubic Zirconia (zirconium oxide)
Types: Synthetic material.
Color: All ranges.
Moh’s hardness: 8.25-8.5
Refractive index: 2.15-2.2
Critical angle: 28°
Specific gravity: 5.7
Fracture: Sub-conchoidal, brittle.
Dispersion: Extremely strong (.06)
Heat sensitivity: Low
Birefringence (double refraction): None
Crystal structure: Isometric
Cutting: Pre-polishing to 8000 will provide a much faster polish.
Polishing: Diamond on hard laps. If polishing is difficult, try tin-lead lap with 50,000 diamond.
Comments: CZ from different manufacturers has different cutting and polishing properties. Also, because of the "skull" process used to make cubic zirconia, every batch can be slightly different in color and cutting characteristics. CZ manufactured in the US, Russia and Britain has the reputation of being more consistent and having less polishing problems.