A hammerstone is the archaeological term used for an object used as a prehistoric hammer, to percussion fractures on another object. Most frequently used in discussion of stone tool working, a hammerstone is likely to be of a rounded cobble of quartzite or other medium-grained material, and to weigh between 400 and 1000 grams. Hammerstone usewear is identified by one or more edges showing battering damage.
In the drawing, a flintknapper holds a hammerstone in his right hand and bangs it against the flint core in his left, making flattish stone flakes come off the core. This process is sometimes called "systematic flaking".