Even if its not, you can cut diagonally from the corners to the stone, with a standard power saw using a masonary blade, for whatever reason the four pieces will give way. You could also rent one of the huge masonary cutters and get close, then, slowly but surely chisel away the remainder. If its a floating slab square form above ground, its going to be easier. If its been post hole dug, plunked in, then of course you have your work cut out for you. I don't claim to be an authority on anything, but I have done this within recent weeks, for someone else, and it went terribly slow but turned out fine. Probably a yard of concrete, involved 50 years old. You can do it ! Lee Creed