Hardness

• Diamonds, whether synthesized or natural, have a top hardness rating of 10 compared to CZ at 8.3. The rating indicates a gemstone's resistance to scratching. CZ may show chipping or rounding of edges. Diamonds do not easily chip and their edges are sharp.
  
  

Light Dispersion

• CZ has a much higher dispersive effect, or fire, than synthesized diamonds. This quality is visible to the naked eye.
  
  

Color

• CZ can turn grayish if exposed to sunlight for extended periods of time. The color of diamonds do not fade with age. Shortwave ultraviolet light will cause CZ to emit a greenish yellow color.
  
  

Refractive Index

• CZ and synthesized diamonds also differ in the refractive index, which measures how much they can bend light rays. The higher the index, the greater the refraction. CZ has an RI of 1.8 to 2.17 compared to a diamond, at 2.417.
  
  

Flaws

• CZ is virtually flawless. Synthesized diamonds can contain inclusions, just like natural diamonds.