How did hammerstones shape Stone Age tools?

In the context of Stone Age anthropology, hammerstones—often referred to as hammerrocks—were fundamental tools used to shape stone implements through the technique of percussion flaking.12

By striking a block of stone with a hand-held hammerstone, early humans could detach flakes from a core or nucleus. This process served two primary purposes:1

• Core Tool Production: Hammerstones were used to fashion large, rudimentary tools, such as the chopper, which remained in use for approximately 2 million years.2
• Roughing Out: They were used to "block in" large tool blanks, creating the basic shape of an implement before finer techniques were applied to achieve a final form.2

The hammerstone technique is characterized by the production of short, deep flake scars. Because the hammerstone is hard, the force of the blow creates a distinct "bulb of percussion" on the detached flake, marking the point of impact. While effective for initial shaping, this method was often followed by more refined techniques, such as the use of softer "hammers" made of wood, bone, or antler, to create sharper, more uniform cutting edges.21