Hello,
Sorry for my late entry to your contest.
I went a different direction and tried for something a bit more conceptual.
Working from your idea of progression form stone -> something more green / sustainable. I simply tried to visualise that concept.
Please note colors and typeface can easily be swapped if you want to see others, just let me know.
Thanks,
Owen.
#169 print version (flat colours)
#172 web version (soft gradients)
#171 still works well in black and white (your logo will inevitably have to appear in b&w at some point)