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Sand

2007 Schools Wikipedia Selection. Related subjects: Geology and geophysics

   Patterns in the sand
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   Patterns in the sand

   Sand is a granular material made up of fine rock particles. Sand is a
   naturally occurring, finely divided rock, comprising particles or
   granules ranging in size from 0.0625 (or ^1⁄[16]) to 2 millimeters. An
   individual particle in this range size is termed a sand grain. The next
   smaller size class in geology is silt: particles below 0.0625 mm down
   to 0.004 mm in size. 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 feels gritty when rubbed between the fingers
   (silt feels like flour). 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). These sizes are based on the
   Φ sediment size scale, where size in Φ = -log base 2 of size in mm. On
   this scale sand is from Φ = -1 to 4, with the divisions between
   sub-categories at whole numbers.

Constituents of sand

   Sand under a scanning electron microscope
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   Sand under a scanning electron microscope
   Close up of black volcanic sand
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   Close up of black volcanic sand

   The most common constituent of sand, in inland continental settings and
   non- tropical coastal settings, is silica (silicon dioxide, or SiO[2]),
   usually in the form of quartz, which, because of its chemical inertness
   and considerable hardness, is quite resistant to weathering. However,
   the composition of sand varies according to local rock sources and
   conditions. The bright white sands found in tropical and subtropical
   coastal settings are ground-up limestone. Arkose is a sand or sandstone
   with considerable feldspar content which is derived from the weathering
   and erosion of a (usually nearby) granite. Some locations have sands
   that contain magnetite, chlorite, glauconite or gypsum. 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 colour, 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 colour. Sand
   deposits in some areas contain garnets and other resistant minerals,
   including some small gemstones.

Transport

   Sand is transported by wind and water and deposited in the form of
   beaches, dunes, sand spits, sand bars, of the like. In most deserts,
   sand is a dominant constituent of the soil.

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. It is called sharp sand in the building trade
   where it is preferred for concrete mixing, and in gardening where it is
   used as a soil amendment to loosen clay soils. 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 sorting tower at a gravel extraction pit.
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   Sand sorting tower at a gravel extraction pit.
     * 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 sometimes mixed with paint to create a textured finish for
       walls and ceilings or a non-slip surface.

     * Sandy soils are ideal for certain crops such as watermelons,
       peaches, and peanuts and are often preferred for intensive dairy
       farming because of their excellent drainage characteristics.

     * Sand is used in landscaping, it is added to make small hills and
       slopes (e.g. for making golf courses).

     * It is the principal component in glass manufacturing.

     * It is often transported to popular beaches where seasonal tides
       sweep its original sand under the sea.

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

     * Sand castle building is a popular activity and there are even
       competitive sand castle building competitions (See sand art and
       play).

     * Sand animation is a type of performance art and a technique for
       creating animated films.

     * Aquaria are often lined with sand instead of gravel, this is a low
       cost alternative which some argue is better than gravel.

     * Railroads use sand to improve the traction of the rails.

     * Some people eat sand on a daily basis in order to stay fit &
       =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. 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 over long periods of time. Material
   safety data sheets (MSDS) for silica sand state that "excessive
   inhalation of crystalline silica is a serious health concern" .

   Retrieved from " http://en.wikipedia.org/wiki/Sand"
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   with only minor checks and changes (see www.wikipedia.org for details
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