Play with the TIR and Ray Depth. Sorry I don't have some settings for you to start with, but I know that the TIR in concert with the Ray Depth and Refraction is the way to simulate Gem stones.

This is not my "second childhood". I'm not finished with the first one yet.

Time flies like an arrow; fruit flies like a banana.

"I'd like to die peacefully in my sleep like my grandfather....not screaming in terror like the passengers on his bus." - Jack Handy