Millstones or mill stones are used in windmills and watermills, including tide mills, for grinding wheat or other grains. The type of stone most suitable for making millstones is a siliceous rock called buhrstone (or burrstone), an open-textured, porous but tough, fine-grained sandstone, or a silicified, fossiliferous limestone. In some sandstones, the cement is calcareous. Types Millstones used in Britain were commonly of two types: Derbyshire Peak stones of grey millstone grit, cut from o… (More on Millstone)