Cubic zirconia (CZ) is the cubic crystalline form of zirconium dioxide (ZrO2). It is hard, optically flawless, and usually colorless, though available in many colors. Key differences include:

• Hardness: CZ has a rating of approx 8 on Mohs scale vs. 10 for diamond.
• Specific Gravity: CZ is about 1.7 times denser than diamond.
• Refractive Index: CZ (2.15-2.18) vs. Diamond (2.42).
• Dispersion: CZ (0.058-0.066) exceeds diamond's (0.044), creating more "fire".
• Color: CZ is often entirely colorless (D grade equivalent), whereas most diamonds have slight yellow/brown tinges.
• Thermal Conductivity: CZ is a thermal insulator, while diamond is a superior conductor.