A steel tool, one end of which has a flat square surface used as a hammer, for breaking bricks, driving nails, etc.; the other end forms a chisel peen used for dressing bricks.
If you have to tweak a piece, chip away edges slowly with a glancing blow of a brick hammer. (Be sure to wear safety glasses when cutting or chipping brick and stone.) Take off too much and you'll break the stone--usually in the wrong spot!
If a piece is too big after you cut it, chip the edge off with a brick hammer to fit.