Grains of rock and mineral with sizes between 63 µm and 2 mm (0·00250·079 in), formed by the physical weathering of rocks, and composed of resistant minerals (usually quartz) not destroyed during weathering. Black sand, containing volcanic rock, and coral sand also occur. Accumulations of sand can be formed by the action of waves on coastal beaches, and by the wind in deserts. Quartz-rich sand is used as an industrial source of silica for glass-making and in cement.
Sand is a naturally occurring, finely divided rock, comprising particles or granules ranging in size from 0.0625 (or 1⁄16) to 2 millimeters. The next larger size class above sand is gravel, with particles ranging from 2 mm up to 64 mm (see grain size for standards in use). Sand is commonly divided into five sub-categories based on size: very fine sand (1/16 - 1/8 mm), fine sand (1/8 mm - 1/4 mm), medium sand (1/4 mm - 1/2 mm), coarse sand (1/2 mm - 1 mm), and very coarse sand (1 mm - 2 mm).Constituents of sand
The most common constituent of sand, in inland continental settings and non-tropical coastal settings, is silica (silicon dioxide), usually in the form of quartz, which, because of its chemical inertness and considerable hardness, is quite resistant to weathering. Arkose is a sand or sandstone with considerable feldspar content which is derived from the weathering and erosion of a (usually nearby) granite. Sands rich in magnetite are dark to black in color, as are sands derived from volcanic basalts. The chlorite-glauconite bearing sands are typically green in color, as are sands derived from basalts (lavas) with a high olivine content. The gypsum sand dunes of the White Sands National Monument in New Mexico are famous for their bright, white color.
Transport
Sand is transported by wind and water and deposited in the form of beaches, dunes, sand spits, sand bars, of the like.
Study of sand
Study of individual grains can reveal quite a bit of historical information as to the origin, kind of transport, etc of the grain. Quartz sand that is recently weathered from granite or gneiss quartz crystals will be angular. Sand that is erosion transported long distances by water or wind will be rounded, with characteristic abrasion patterns on the surface of the grains.
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. Molding sand, also known as foundry sand, is moistened or oiled and then shaped into molds for sand casting. This type of sand must be able to withstand high temperatures and pressure, allow gases to escape, have a uniform, small grain size and be non-reactive with metals. Graded sand is used as an abrasive in sandblasting and is also used in media filters for filtering water. Brick manufacturing plants use sand as an additive with a mixture of clay and other materials for manufacturing bricks. Sand is used in landscaping, it is added to make small hills and slopes (e.g. Sand castle building is a popular activity and there are even competitive sand castle building competitions (See sand art and play). http://www.newkerala.com/news4.php?action=fullnews&id=46736)Hazards of sand
While sand is generally harmless, one must take care with some activities involving sand such as sandblasting. Bags of silica sand now typically carry labels warning the user to wear respiratory protection and avoid breathing the fine silica dust because of this. Material safety data sheets (MSDS) for silica sand state that "excessive inhalation of crystalline silica is a serious health concern" .
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