Although the smoothest way to cut stone is with a jack hammer or a stone cutter, there is another way to do it if you don't have access to these tools. A chisel and a hammer are the traditional tools for cutting stone. With these two simple tools, you can cut rocks as hard as flagstone.
Put on safety glasses and heavy gloves before you begin. Stone shards can fly when you cut stone, so eye and hand protection are imperative.
Lay the stone over the bag of gravel or sand.
Use chalk to mark the line where you want to cut the stone. Make sure to mark all sides of the stone.
Score the stone along the chalk line with the chisel, using moderate pressure.
Place the chisel along the scored line and lightly tap it with the hammer. Do this every few centimeters along the line. Repeat until the stone breaks along the scored line.
If the chisel's edges begin to curl, keep it smooth by grinding it periodically.
Do not bang on the chisel with a lot of force. This may cause the stone to shatter rather than breaking cleanly.