I tried it the other day on some kind of granite boulder, that stuff really doesn't drill or chisel easily (I managed to drill down and get the chisel stuck for a minute though). I also tried drilling shallower holes and slamming a spiked chisel between them, but it ricochetted and flew back at me (which I suspected might happen, just not that fast). So I would have had to pulverize it with a chipping hammer for hours and hours, or get a powered version of one (but didn't need to break it up that badly).