I really like it! Are you trying to get a more weathered looking stone, or did you just mean the stone wasn't "stony" enough? I imagine you're using Bryce 5 or so, (way above my version at least) so I can't be that much help, just thought I'd say it's a nice model and render ;) On the weathered stone note though, I made a rather interesting erroded pottery texture using the pitted concrete material in Bryce 3's preset library. Never underestimate the presets for using as starting points ;)