The stone has definitely been altered by man, but not putting down this find an this is JMO. I don't buy into the sinew theory of splitting the fiber with a stone in that shape. I have handled whitetail, elk, moose, mule deer and even Emu sinew an you don't have to strip it. All you have to do with the leg tendon is let it dry an hit it with a stone an it will break up into threads. As for back straps clean the meat off let it dry an you can twist it with your hands working it back an forth and it will divide into very nice pieces of thread. Just my thoughts due to the fact that I have handled 100's of pounds of sinew.