The term tool stone has multiple meanings. In archaeology, a tool stone is a type of stone that is used to manufacture stone tools. Alternately, the term can be used to refer to 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.
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.
In the contemporary diamond industry a tool stone is a diamond attached to a pole, used to work a second diamond.
In metal-working fragments of diamond are bonded to the edge of cutting tools.
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