14. Diamond vs Cubic zirconium.

The different between a diamond and a cubic zirconium.

Well-cut cubic zirconium can compete with diamond, but when held side-by-side with a diamond, there is a visual difference. A colorless cubic zirconium tends to cast some rainbow reflections within it, called 'fire'. A colorless or near-colorless diamond doesn't tend to -- most of the sparkle is shades of gray and white. Cubic zirconium is manufactured in numerous different colors including different shades of pink, yellow, purple, blue, orange, red, brown, colorless and even opaque black. CZ is an 8½ on the Mohs hardness scale, about the same as topaz. CZ is also much more dense than diamond with a specific gravity of 5.8 while diamond is just 3.5. (In other words, a piece of CZ is going to weigh about 75% more than a piece of diamond of identical mass. Some CZ is grown with different formulas, which means the 75% figure isn't always true.) Diamond has a refractive index of 2.42. CZ has a refractive index of about 2.15, making it brighter than quartz, topaz, corundum and other materials, but not as bright as diamond.

Reference : http://famousdiamonds.tripod.com/faq.html