A long time ago (last March) in a galaxy far far away (my pre-Mac computer days), I published an article about Phoenix's gem system.
I really like gems, and I have always loved complicated generation systems for them. This love was inspired by 2nd edition D&D.
That being said, it doesn't work for my new project. My new project requires a whittled down ruleset. So, I had to come up with something simple for gems.
First, I combined gems with jewelry. The theme I'm working with is fantasy, but it doesn't require a bunch of details on such objects.
Each treasure includes a definition for its Jewel dice (dJ). So it might be d4, d6, d10, 3d6... whatever is appropriate. It can have multiples, like 2dJ or 3dJ, which means there are 2 or 3 rolls on the Jewel table.
This is the Jewel table. Recall that I use a silver-piece based economy, and also recall that I use exploding dice (so a d4 roll can get a 5 or higher sometimes). Also, 1 GP = 100 SP for me.
Detailed descriptions of the gem types, filigrees, et al can be provided by the GM, but in the game I'm working on, I think it will usually come out something more like, "You find a crappy amulet on that dead gremlin."
This is the sort of whittling I've been doing, and I'm happy with the results so far. I can't wait to play some games and share my results.