The rocks that work best for stone tool making are called siliceous rocks , which are rocks made of silicone dioxide. The most common type of siliceous rock used for stone tools is called chert or flint . Siliceous rocks break predictably because they have few impurities. Chert can be shaped by either percussion flaking or pressure flaking , which are the oldest types of stone tool making. When the toolmaker uses the shaped core as a tool, it is called a core tool .
People also use the flakes to cut with.
These are called flake tools . In order to remove a flake off a piece of chert, the toolmaker applies a blow to a specific point on the rock, which is called a percussive blow . Because chert has few impurities, the energy spreads from the contact point outward without anything to stop it, in the shape of a cone. The energy moves in a wave and is called a conchoidal fracture pattern because from the side, the cone looks like a shell. This happens every time a toolmaker strikes a core with a hammerstone.