Sparkle Color

• Instantly, CZ and diamonds can be deciphered by color. When light hits CZ, it refracts several different colors. The colors range from those in a rainbow all at once. When light hits a natural diamond, it gives off white sparkles of light. No colors should be seen.
  
  

Stone Color

• Though a CZ sparkle is colorful, the stone is always white. This is rare in diamonds. Colorless diamonds are extremely rare and more expensive. Diamonds will almost always have a yellow tint to them. Even nearly colorless diamonds--more expensive diamonds that are a little less rare--still have yellow in them. The more yellow, the lower the cost.
  
  

Flaws

• CZ stones are always flawless. The same is never true in a diamond. Though a jeweler's loupe (magnifying glass) must be used to see flaws within a diamond, they are there. They will never be in the man-made CZ.
  
  

Strength

• The Mohs Scale of Hardness tests the hardness of stones from weakest to strongest, with diamonds being strongest. Diamonds cannot be chipped, scratched or damaged by any other stone, which makes it a 10.0 on the Mohs Scale. Talc is the weakest, and can be easily crumbled by a fingernail. CZ rates as an 8.5 on the Mohs Scale and can easily be chipped or scratched.
  
  

Cost

• If looking strictly for the cheapest route, go CZ. CZ is also almost always mounted in cheaper gold- or silver-plated metals, not actual gold, silver or white gold. It is unlikely that a high-carat ring will have a CZ as the main stone.
  
  

Heat Resistance

• Get the correct size CZ the first time. A jeweler's torch, used to re-size rings, will severely crack the stone and ruin it. Diamonds are strong enough to resist the heat from a jeweler's torch, and rings with them can easily be re-sized. Also, because CZ is mounted in more inexpensive metals, it is important to be careful not to ruin the metal by heat, too.
  
  

Size

• CZ comes in a range of very large sizes, which diamonds cannot reasonably achieve. CZ stones can be as big as 8 carats. Many diamond sizes come in fractions, not large whole numbers. If you're going for the bigger stone, CZ is a better bet, especially when dealing with reasonable cost.