Ground stone tools are shaped by two separate processes, by use, or intentionally shaped to conform to a desired form. Ground stone materials were intentionally selected because they are not conducive to conchodial fracture. Coarse-grained or coarse crystalline materials (such as basalt, andesite, rhiolite, granite, sandstone, silicified sandstone, quartzite, among others) depending on what was locally available in the outcrops or gravels, were used as grinding implements such as grinding basins (cairns, metates, mortars) and grinding stones (manos, mullers, pestles). These types of artifacts acquired their shapes through use. They were initially shaped by pecking and grinding, using material of equal density as a pecking stone. Pecking creates tiny impact craters that remove bits and pieces of material with each blow. Pecking is time-consuming, but an efficient method of shaping a coarse rock preform. Once shaped, the grinding basin and grinding stone assume their characteristic use-shape which is the form that most often appears archaeologically.
Artifacts intentionally shaped by pecking, grinding, and polishing include a very wide variety of tool forms. Functional tools such as axes, celts, and adzes, for example, may be made of very hard crystalline material, including igneous rocks such as granites, porphyry, and basalt, or metamorphic rocks such as quartzite or metamorphic sandstone. The density of the rock served as an advantage for such tools used in heavy cutting and chopping tasks because of their resistance to fracture.
See also: Lithics: Analysis, Use Wear.
World History
