Sand

Sand is a naturally occurring material made up of small granules of rock or mineral fragments. The size of sand granules ranges between silt (the finer grade) and small pebbles (the coarser grade). Geologists typically define sand grains as having diameters between 0.06 mm and 2 mm, although definitions vary depending on the classification systems used.

Sand forms from the breakdown of rock over long periods. Water, wind, ice, and temperature changes break rock into small fragments. These particles are carried by rivers, ocean currents, and wind, and then accumulate in specific locations such as beaches, desert floors, river valleys, and sea beds.

Composition

The most common mineral in sand is quartz, because quartz resists both chemical and physical weathering. Other sand may contain feldspar, weathered rock fragments, and organic material such as shell fragments or coral. Some beaches on volcanic islands have dark sand derived from volcanic rock, while other areas have light sand composed of coral and calcium carbonate.

Grain size and shape

Sand grains are classified by size (from very fine to very coarse) and shape (rounded or angular). Wind-transported sand is typically well-sorted and rounded, because long transport smooths the edges. River sand is typically poorly sorted and mixed. These features tell scientists how material was transported and where it came from.

Economic uses

Sand is one of the most abundant naturally occurring materials extracted worldwide. It is used in the production of concrete (made with stone and gravel), road construction, landfill, and glassmaking. Glass-quality sand requires pure quartz. Because desert sand is present in vast quantities, its grains are very rounded and therefore unsuitable for concrete; this is why sand for construction is extracted from rivers, valley floors, and the sea.

Environmental impact

Uncontrolled sand extraction from rivers and beaches can harm the environment: lowering of river beds, coastal erosion, and damage to aquatic ecosystems. Many countries have adopted coastal regulations and restrictions, although illegal sand markets exist in some regions.