Inarchaeology, atool stone is a type of stone that is used to manufacturestone tools,[1]or tools that use stone as raw material.[2]
Generally speaking, tools that require a sharp edge are made usingcryptocrystalline materials that fracture in an easily controlledconchoidal manner.[1]Cryptocrystalline tool stones includeflint andchert, which are fine-grainedsedimentary materials;rhyolite andfelsite, which areigneousflowstones; andobsidian, 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, seelithic reduction.
Large-grained materials such asbasalt,granite andsandstone may also be used as tool stones, but for a very different purpose: they are ideal forground stoneartifacts. Whereas cryptocrystalline materials are most useful for killing and processing animals, large-grained materials are usually used for processing plant matter. Their rough faces often make excellent surfaces for grinding plant seeds. With much effort, some large-grained stones may be ground down intoawls,adzes, andaxes.