Wow, thank you BManx2000, that looks a great deal better than the picture I had acquired. It seems like it will fit a lot better in the map, that's for sure.
I also agree with your thoughts on making the map darker. It will need to be fairly dark, in order to capture the better look of the crystals.
Polys would work for larger crystals, indeed. I just wish I could help more in the creation of this map. You're all too kind for helping me so.
I'll see if I can find a background image, maybe something along the lines of the inner hull of a geode.
Edit: I found some pretty interesting pictures, not all of them of real, live geodes either, but here's the gallery:
Geode Rendition
Several pictures of crystals and geode-related structures.
This would be cool if the seam weren't quite so obvious.
Amazing, how large these things can get.
That's all I have found in terms of good backgrounds and scenery so far. I'll see what I can do, however.