A Neolithic ground stone.
In archaeology, ground stone is a category of stone tool formed by the grinding of a coarse-grained tool stone, either purposely or incidentally. Ground stone tools are usually made of basalt, rhyolite, granite, or other macrocrystalline igneous stones whose coarse structure makes them ideal for grinding other materials, including plants and other stones. In Europe the adoption of ground stone technology is associated closely with the Neolithic. In the Levant ground stones appear in Mesolithic 2 (Natufian).
Some ground stone tools are incidental, caused by use with other tools: manos, for example, are hand stones used in conjunction with metates and other grinding slabs (querns), and develop their ground surfaces through wear. Other ground stone tools include adzes, celts, and axes, which are manufactured using a labor-intensive, time-consuming method of repeated grinding against a harder stone or with sand, often using water as a lubricant. These tools are often made using durable finer-grained materials rather than coarse materials. In the North American arctic, tools made of ground slate were used by the Norton, Dorset, and Thule tool cultures. Common forms of these tools were projectile points and ulus.