What is the best way to emulate a gem surface in a material?

I’m trying to emulate the appearance of a gemstone with a material, and am not sure how to go about it. One suggested method involved getting a lightvector which doesn’t seem possible in normal circumstances from what I can tell. I’m fairly unexperienced with material creation; I just need a nice looking gem material; it doesn’t need to be nearly as complicated as this picture, but I’m going for a similar effect: