The Meaning of Life, the Universe, and Everything.
Interesting concept, but the textures look strange, to say the least.
A little work on the texturing would go a long way here, I think. If you need any help with that, shoot me a PM. I can do recolor textures fairly well. Also, why not name them Ruby, Sapphire, Emerald/Peridot, and Onyx? Just sounds better than having Crystal everything. Anyway, that's this novice modder's two cents.
Looks like you've got a good start going here, at the very least. Good luck.