Matted Stone Finish

I'd like to make a finish on a cake that looks as much like stone as possible (this is the fairy-well cake for those that read that post -- I've got the gelatin sorted out, but I'd like to improve on the finish).  I'm aiming for realism

I was imagining I could somehow blow icing sugar on top of some darker cream to give a matte look, and then using a carving chisel to etch out the grout lines.  I'm wondering if anything like this has been done before, and if I could get some hints on how to best go about it.

Thanks

John