In archaeology, a tool stone is a type of stone that is used to manufacture stone tools,or stones used as the raw material for tools. Generally speaking, tools that require a sharp edge are made using cryptocrystalline materials that fracture in an easily controlled conchoidal manner.Cryptocrystalline tool stones include flint and chert, which are fine-grained sedimentary materials; rhyolite and felsite, which are igneous flowstones; and obsidian, a form of natural glass created by igneous processes. These materials fracture in a predictable fashion, and are easily resharpened. For more information on this subject, see lithic reduction.