Tool stone
In
archaeology, a
tool stone is a type of stone that is used to manufacture stone 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.
Large-grained materials, such as basalt, granite, and sandstone, may also be used as tool stones, but for a very different purpose: they are ideal for ground stone artifacts. 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 into awls, adzes, and axes.