**tekmonk:** Even a flat facet (although a single flat polygon is impossible to replicate in the realworld) will produce a caustic depending on the angle the light strikes it and the material applied to the facet.

A coincidence you refer to a ruby image - I done this rough and ready one last night while I was trying out the Gem model just to see how it performed. Needs a better lighting set up and some more render time to get it to photo quality though :-). It uses correct Index Of Refraction data to give a good result - by data I mean the usual IOR value for the gem, plus light dispersion etc.