I agree with Molly and Dorkfish. I zoomed in on the pic, and could see no signs of flaking what so ever. I am pretty sure its just a natural rock. As I have said on here before, Mother nature has a way of making some neat stuff. You can probably find a rock some where in the shape of anything man made. Example, I work with a brick layer that we all call a Boot, thats his nickname. One day while head hunting in a creek, I found a rock in the perfect shape of a boot, took it to work and put it in his tool box. He knew exactly what it was when he opened his box, and we all had a good laugh. I have seen rocks in the shapes of houses cars etc. Sorry for rambling on, but any way thats my opinion on what you have there. Keep looking. John