Millstone
These implements are often called grinding stones. ... an open textured, porous but tough, fine grained sandstone, or a silicified, fossiliferous limestone. In some sandstones, the cement is calcareous. Millstones used in Britain were of several types: Derbyshire Peak stones of grey Millstone Grit, cut from one piece, used for grinding barley; imitation Derbyshire Peak stones are used as ...