Abstract: The device for breaking rocks includes a hollow cylindrical chamber having a closed lower end, a closed upper end and an access aperture in the closed upper end and an outer circumstantial surface. A cylindrical plunger is longitudinally-reciprocally disposed within the interior of the cylindrical chamber, the plunger being has a converging portion and is biased to a retracted position. Four spools are equally disposed around the circumference of the cylindrical plunger, each spool including a converging upper end which is configured to be in slidable contact with the converging portion of the cylindrical plunger. Four hardened inserts are secured to an outer face of an associated spool. Each spool and secured hardened insert is biased to an inner retracted position.