As Andrew says, diamond has a pretty high refractive index which gives lots of fire and color when the light is refracted.

Here's a pretty good page on diamond properties: http://nature.berkel...//wisc/Lect6.html

Diamond (C) Refractive Index = 2.42

Lead Glass (SiO2+PbOx) Refractive Index ~ 1.70 http://en.wikipedia.org/wiki/Lead_glass

Cubic Zirconia (ZrO2) Refractive Index = 2.15–2.18 http://en.wikipedia....ki/Cubic_zirconia

Moissanite (Silicon Carbide) Refractive Index = 2.65-2.69 http://en.wikipedia....n_carbide#Jewelry

The angles of the facets would need to be adjusted as the refractive index changes. There are other differences in the materials that affect how the light is scattered (e.g. birefringence).

HTH a little.

Cheers,
Scott.