Determine where the fieldstone needs to be cut. Mark the cut lines on the fieldstone with a dark marker or pencil.
Place a diamond tipped masonry blade on a circular or tile saw. If you are using a tile saw, you may need to remove the protective cover from the top of the saw so the thick fieldstone can fit through the saw.
Cut the fieldstone with the tile or circular saw. When using a circular saw, prop the fieldstone up on something like a sawhorse while it is cut.
Finish breaking thick pieces of fieldstone with a hammer. In places where the fieldstone is thicker than 1 inch, the saw will not completely cut through it. Use a mallet or hammer to finish breaking the stone to size.