Final answer:
Diamonds sparkle more than other materials due to total internal reflection and a large index of refraction. The facets on diamonds ensure that light can only exit in certain places, creating the sparkle that diamond cutters aim for.
Step-by-step explanation:
Total internal reflection, coupled with a large index of refraction, explains why diamonds sparkle more than other materials. The critical angle for a diamond-to-air surface is only 24.4°, so when light enters a diamond, it has trouble getting back out. Facets on diamonds are specifically intended to make this unlikely, so that the light can exit only in certain places. This results in the concentration of light at these points, creating the sparkle that diamond cutters aim for.