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Sand is a naturally occurring, finely divided rock, comprised of particles ranging in size from 0.063 to 2 mm. An individual particle in this range size is termed a sand grain. The next smaller size class in geology is silt, which are particles below 0.063 mm down to 0.004 mm in size; the next larger size above sand is gravel, which ranges up to 64 mm (see grain size for standards in use).

The most common constituent of sand in inland continental settings and non-tropical coastal settings, is silica (silicon dioxide), often in the form of quartz. However, the composition of sand varies according to local rock sources and conditions. Much of the fine white sand found in coral reef settings, for example, is ground-up coral (limestone) that has passed through the digestion of the parrot fish. Some locations have sands that contain iron, feldspar, or even gypsum.

Sand is transported by wind or water and deposited in the form of beaches, dunes, sand spits, sand bars, and the like. In a desert, sand is a dominant soil type. Sandy soils are ideal for certain crops such as watermelons and peanuts and are often preferred for intensive dairy farming because of their excellent drainage characteristics.

Sand is an example of a class of materials called granular matter.

Uses of sand

Sand is often a principal component of the aggregate used in the preparation of concrete. Sand manufactured at rock crusher plants for use as an aggregate is called mansand. Graded sand is used as an abrasive in sandblasting and is also used in media filters for filtering water.

Sand bags are used for protection against floods and gun fire. They can be easily transported when empty, and filled with local sand.

People, especially children, love to play with sand on a beach or in a sandbox. See sand art and play for details.

Hazards of sand

Bags of sand now typically carry labels warning the user to wear respiratory protection and avoid breathing the fine silica dust. There have been a number of lawsuits in recent years where workers have sought damages after they developed silicosis, a lung disease caused by inhalation of fine silica particles.

People have been severely injured and even killed after digging sand "caves" in large dunes or sandhills and the cave collapsed upon them.

See also