In addition to the shape and cut of a gem, the material it is made of has a major influence on how it looks. This section provides information and suggestions on making your gemstones look natural.

 

Gemstone Properties Color; both normal and variants, for many gemstones, as well as some Bryce presets I have made.
Refractive Index- (RI) Listings for most gemstones, and an demonstration of how the RI can affect a 3D rendering.
   

For more detailed articles on these topics, Bob Keller has several clear, but detailed, explanations available at his site. While these are geared toward actual lapidary situations, they do contain information which can be applied to 3D rendering. Two of the more relevant ones are:

PROPERTIES OF COMMONLY FACETED MINERALS AND MATERIALS

REFRACTIVE INDEX AND CRITICAL ANGLE