The first stone tools, used by our human ancestors, were big rocks used for pounding, like you would use a hammer. Ancient humans figured out that some kinds of rock break in a predictable way, and because of that predictability, they could shape the rock into different forms. Not all rocks break predictably, though. 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 .