Don't want to spoil anyone's modeling fun, but I have a lot of gemstone cut models (100+), in a number of 3d file formats, ready to use at:
http://www.3dlapidary.com

These are based on real cut designs, from people who design gemstones in real-life, made with their permission. The models are free for use by 3d artists, with the request that users credit the cut designer and site source.

I also have a collection of Bryce presets (courtesy of the Riggs sisters) for gemstone materials, and a lot of other useful information concerning real gemstones.

Drop on by.

RosemaryR
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"This...this is magnificent!"
"Oh, yeah. Ooooo. Aaaaah. That's how it starts.
Then, later, there's ...running. And....screaming."