A tool making technique in which a brittle rock (e. G. , obsidian, flint, chert, and basalt) that will potentially be an artifact is struck with a heavy glancing blow from another dense rock (i.e., a hammerstone) in order to cause a flake to be removed. An artifact can be shaped by carefully and systematically directing the percussion blows with the hammerstone. Percussion flaking works when a sufficiently large shock wave is directed into the target rock so that the elastic limit of the material is exceeded. This causes one or more flakes to be broken off. See pressure flaking.