Hammerstones are the most common flintknapping tool in the archaeological record.  These tools were often highly prized because it can be difficult to find a stone of the appropriate shape, weight, and material to suit various flaking techniques.  Hammerstones of hard materials, such as igneous or metavolcanic rocks, were used for removing flakes by striking in from the edge of the core (called ‘off-edge percussion’); and softer stones, such as limestone or sandstone, were used to remove flakes by striking right onto the edge of the core (called ‘on-edge percussion’).  The effects from using soft hammerstones can be similar to the effects from using soft organic hammers, such as antler.