“Hammerstone” is the archaeologist’s term for a hand-held stone that shows battering on one or more surfaces, from coming into contact with another hard object:  presumably, the harder the object, the heavier the battering.  Smaller, fist-sized hammerstones often were used for flaking obsidian, chert, and other raw materials into tools.

It was important for the hammerstone to be made of relatively hard material, so that it would not break when striking other objects.  Quartz, quartzite, and basalt make particularly sturdy hammerstones, but these materials are not available in all areas of California, and so stones like chert and sandstone also were used.

	The typical hammerstone shows flattening, crushing, or flake removal along one or more edges.  Note how the texture of the battered edge is different from the rest of the piece.
Sometimes the use-wear is visible as areas of the stone where the exterior rind or cortex has been battered away (left).  Also note the whitish crushed areas (right).