Sand is a collection of mineral particles, with diameters in the range 0.125–2 millimeters, worn away from rock by erosion. It can be graded according to particle size: fine (0.125–0.25 millimeter); medium (0.25–0.5 millimeter); coarse (0.5–1.0 millimeter); and very coarse (1–2 millimeters). Sands result from erosion by glaciers, winds, or ocean or other moving water. Their chief constituents are usually quartz and feldspar. Black sand (containing volcanic rock) and coral sand can also occur.

The term arenaceous means something that is associated with sand; most commonly used to describe types of sedimentary rock. In botany, an arenaceous plant is one that thrives in sandy soil; while in zoology, arenaceous animals live in sand. The shells of some microscopic animals, which consist mainly of sand particles, are also described as being arenaceous.

See also sandstone.