I think there must be an art to photographing crystals.
My goal today was a quick indoor tripod shot of a crystal sparkling in the morning light. I could see the sparkles, even occasional starbursts at certain angles. I used a small aperture (f/22-29 most of the time) and a slow enough shutter speed for correct exposure- but no starbursts. Lots of bokeh, however . . .
Good focus was difficult for me today too, even though I was focusing manually. Finally, I took the crystal outside, because the good indoor morning light was going away- and I got a pretty good exposure with the front part of the crystal in focus. No starbursts, however.
f/29, 1/160, ISO 250, 85mm
melinda anderson photography 
This is beautiful; nice composition that almost looks like glacier peaks. They say a small aperture makes for star bursts but you might try placing a piece of mesh or screen over your lens and experimenting. I managed to get some starbursts using a piece of screen. Try this: