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Close-up of sand from a beach in Vancouver, showing a surface area of (approximately) between 1-2 square centimetres.
Heavy minerals (dark) in a quartz beach sand (Chennai, India).

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.

As the term is used by geologists, sand particles range in diameter from 0.0625mm (or 116 mm, or 62.5 micrometers) to 2 millimeters. An individual particle in this range size is termed a sand grain. The next larger size class above sand is gravel, with particles ranging from 2 mm up to 64 mm (see particle size for standards in use). The next smaller size class in geology is silt: particles smaller than 0.0625 mm down to 0.004 mm in diameter. The size specification between sand and gravel has remained constant for more than a century, but particle diameters as small as 0.02 mm were considered sand under the Albert Atterberg standard in use during the early 20th century. A 1953 engineering standard published by the American Association of State Highway and Transportation Officials set the minimum sand size at 0.074 mm. A 1938 specification of the United States Department of Agriculture was 0.05 mm.[1] Sand feels gritty when rubbed between the fingers (silt, by comparison, feels like flour).

ISO 14688 grades sands as fine, medium and coarse with ranges 0.063 mm to 0.2 mm to 0.63 mm to 2.0 mm. In the United States, sand is commonly divided into five sub-categories based on size: very fine sand (116 - 18 mm diameter), fine sand (18 mm - 14 mm), medium sand (14 mm - 12 mm), coarse sand (12 mm - 1 mm), and very coarse sand (1 mm - 2 mm). These sizes are based on the Krumbein phi scale, where size in Φ = -log base 2 of size in mm. On this scale, for sand the value of Φ varies from -1 to +4, with the divisions between sub-categories at whole numbers.

Contents

Constituents

Sand from Pismo Beach, California. Components are primarily quartz, chert, igneous rock and shell fragments. Scale bar is 1.0 mm.
Close up of black volcanic sand from Perissa, in Santorini, Greece

The most common constituent of sand, in inland continental settings and non-tropical coastal settings, is silica (silicon dioxide, or SiO2), usually in the form of quartz, which, because of its chemical inertness and considerable hardness, is the most common mineral resistant to weathering.

The composition of sand is highly variable, depending on the local rock sources and conditions. The bright white sands found in tropical and subtropical coastal settings are eroded limestone and may contain coral and shell fragments in addition to other organic or organically derived fragmental material.[2] The gypsum sand dunes of the White Sands National Monument in New Mexico are famous for their bright, white color. Arkose is a sand or sandstone with considerable feldspar content, derived from the weathering and erosion of a (usually nearby) granitic rock outcrop. Some sands contain magnetite, chlorite, glauconite or gypsum. Sands rich in magnetite are dark to black in color, as are sands derived from volcanic basalts and obsidian. Chlorite-glauconite bearing sands are typically green in color, as are sands derived from basaltic (lava) with a high olivine content. Many sands, especially those found extensively in Southern Europe, have iron impurities within the quartz crystals of the sand, giving a deep yellow color. Sand deposits in some areas contain garnets and other resistant minerals, including some small gemstones.

Environments

Sand from Coral Pink Sand Dunes State Park, Utah. These are grains of quartz with a hematite coating providing the orange color. Scale bar is 1.0 mm.

Sand is transported by wind and water and deposited in the form of beaches, dunes, sand spits, sand bars and related features. In environments such as gravel-bed rivers and glacial moraines it often occurs as one of the many grain sizes that are represented. Sand-bed rivers, such as the Platte River in Nebraska, USA, have sandy beds largely because there is no larger source material that they can transport. Dunes, on the other hand, are sandy because larger material is generally immobile in wind, and are a distinctive geographical feature of desert environments.

Study

An electron micrograph showing grains of sand
Photomicrograph of a volcanic sand grain; upper picture is plane-polarized light, bottom picture is cross-polarized light, scale box at left-center is 0.25 millimeter.

The study of individual grains can reveal much historical information as to the origin and kind of transport of the grain. Quartz sand that is recently weathered from granite or gneiss quartz crystals will be angular. It is called grus in geology or sharp sand in the building trade where it is preferred for concrete, and in gardening where it is used as a soil amendment to loosen clay soils. Sand that is transported long distances by water or wind will be rounded, with characteristic abrasion patterns on the grain surface. Desert sand is typically rounded.

People who collect sand as a hobby are known as arenophiles or psammophiles.

Uses

At 300 km/h, an ICE 3 (DB class 403) releases sand from several bogies to the rails.
Sand sorting tower at a gravel extraction pit.
  • Agriculture: Sandy soils are ideal for crops such as watermelons, peaches, and peanuts and their excellent drainage characteristics make them suitable for intensive dairy farming.
  • Aquaria: Sand makes a low cost aquarium base material which some believe is better than gravel for home use.
  • Artificial reefs: Geotextile bagged sand can serve as the foundation for new reefs.
  • Beach nourishment: Governments move sand to beaches where tides, storms or deliberate changes to the shoreline erode the original sand.[3]
  • Brick: Manufacturing plants add sand to a mixture of clay and other materials for manufacturing bricks.
  • Car Engine Disablement Sand is also used in addition to Sodium Silicate to inexpensively, quickly, and permanently disable automobile engines.
  • Cob: Coarse sand makes up as much as 75% of cob.
  • Concrete: Sand is often a principal component of this critical construction material.
  • Glass: Sand is the principal component in common glass.
  • Landscaping: Sand makes small hills and slopes (for example, in golf courses).
  • Paint: Mixing sand with paint produces a textured finish for walls and ceilings or non-slip floor surfaces.
  • Railroads: Train operators use sand to improve the traction of wheels on the rails.
  • Roads: Sand improves traction (and thus traffic safety) in icy or snowy conditions.
  • Sand animation: Performance artists draw images in sand. Makers of animated films use the same term to describe their use of sand on frontlit or backlit glass.
  • Sand casting: Casters moisten or oil molding sand, also known as foundry sand and then shape it into molds into which they pour molten material. 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.
  • Sand castles: Shaping sand into castles or other miniature buildings is a popular beach activity.
  • Sandbags: These protect against floods and gun fire. The inexpensive bags are easy to transport when empty, and unskilled volunteers can quickly fill them with local sand in emergencies.
  • Sandblasting: Graded sand serves as an abrasive in cleaning, preparing, and polishing.
  • Water filtration: Media filters use sand for filtering water.
  • Zoanthid "skeletons": Animals in this order of marine benthic cnidarians related to corals and sea anemones, incorporate sand into their mesoglea for structural strength, which they need because they lack a true skeleton.

Hazards

A stingray about to bury itself in sand

While sand is generally non-toxic, sand-using activities such as sandblasting require precautions. Bags of silica sand used for sandblasting now carry labels warning the user to wear respiratory protection to avoid breathing the resulting fine silica dust. Material safety data sheets (MSDS) for silica sand state that "excessive inhalation of crystalline silica is a serious health concern".[4]

In areas of high pore water pressure sand and salt water can form quicksand, which is a colloid hydrogel that behaves like a liquid. Quicksand produces a considerable barrier to escape for creatures caught within, who often die from exposure (not from submersion) as a result.

Environmental Issues

Sand's many uses require a significant dredging industry, raising environmental concerns over fish depletion, landslides, and flooding. Countries such as China, Indonesia, Malaysia and Cambodia ban sand exports, citing these issues as a major factor.[5]

See also

References

  1. ^ Urquhart, Leonard Church, "Civil Engineering Handbook" McGraw-Hill Book Company (1959) p.8-2
  2. ^ Seaweed also plays a role in the formation of sand
  3. ^ Importing Sand, Glass May Help Restore Beaches : NPR
  4. ^ Simplot
  5. ^ "The hourglass effect". October 8, 2009. http://www.economist.com/world/asia/displaystory.cfm?story_id=14588255. Retrieved October 14, 2009. 

External links


1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

SAND. When rocks or minerals are pulverized by any agencies, natural or artificial, the products may be classified as gravels, sands and muds or clays, according to the size of the individual particles. If the grains are so fine as to be impalpable (about oT6 in. in diameter) the deposit may be regarded. as a mud or clay; if many of them are as large as peas the rock is a gravel. Sands may be uniform when they have been sorted out by some agency such as a gentle current of water or the wind blowing steadily across smooth arid lands, but usually they vary much both in the coarseness of their grains and in their mineral composition. The great source of natural sands is the action of the atmosphere, frost, rain, plants and other agencies in breaking up the surfaces of rocks and reducing them to the condition of fine powder; in other words sands are ordinarily the product of the agencies of denudation operating on the rocks of the earth's crust. Not all, however, are of this kind, for a few are artificial, like the crushed tailings produced in the extractions of metals from their ores; there are also volcanic sands which have originated by explosions of steam in the craters of active volcanoes.

A great part of the surface of the globe is covered by sand. In fertile regions the soil is very often of a sandy nature; though most soils are mixtures of sand with clay or stones, and may be described as loams rather than as sands. Pure sandy soils are found principally near sea-coasts where the sand has been blown inwards from the shore, or on formations of soft and friable sandstone like the Greensand. The soil of deserts also is often arenaceous, but there the finer particles have been lifted and borne away by the wind. Accumulations of sand are found also in some parts of the courses of our rivers, very often over wide stretches of the seashore, and more particularly on the sea bottom, where the water is not very deep, at no great distance from the land.

Of the rock-making minerals which are common on the earth's crust only a limited number occur at all frequently in sand deposits. For several reasons quartz is by far the commonest ingredient of sands. It is a very abundant mineral in rocks and is comparatively hard, so that it is not readily worn down to a very fine muddy paste. It also possesses practically no cleavage, and does not split up naturally into thin fragments. If we add to this that it is nearly insoluble in water and that it does not decompose, but preserves its freshness unaltered after long ages of exposure to weathering, we can see that it has all the properties necessary for furnishing a large portion of the sandy material produced by the detrition of rock masses. With quartz there is often a small amount of felspar (principally microdine, orthoclase and oligoclase), but this mineral, though almost as common as quartz in rocks, splits up readily on account of its cleavage, and decomposes into fine, soft, scaly aggregates of mica and kaolin, which are removed by the sifting action of water and are deposited as muds or clays. Small plates of white mica, which, though soft and very fissile, decompose very slowly, are often mingled with the quartz and felspar. In addition to these, all sands contain such minerals as garnet, tourmaline, zircon, rutile and anatase, which are common rock-forming minerals, both hard and resistant to decomposition. Among the less common ingredients are topaz, staurolite, kyanite, andalusite, chlorite, iron oxides, biotite, hornblende and augite, while small particles of chert, felsite and other fine-grained rocks appear frequently in the coarser sand deposits.

Shore sands and river sands, which have not been transported for any great distance from their parent rocks, often contain minerals that are too soft or too readily decomposed to persist. In the Lizard district of Cornwall the sands at the base of cliffs of serpentine are rich in olivine, augite, enstatite, tremolite and chromite. Near 'volcanic islands such minerals as biotite, hornblende, augite and zeolites may form a large portion of the local sand deposits. In marine sands also organic substances are almost universally present, either fragments of plants or the debris of calcareous shells, in fact many sands. consist almost entirely of such fragments (shell sands). Around coral islands there are often extensive deposits of comminuted coral (coral sands), mixed with which there is a varying proportion of broken skeletons of calcareous algae, sponge-spicules and other debris of organic origin. The Greensands which are widely distributed over the floor of the oceans, in places where the continental shelf merges into the greater depths, owe their colour to small 'rounded lumps of glauconite.

Among the accessory ingredients of sands which are of great value and interest are the precious metals, especially gold and platinum. These are found usually in the lower parts of the sand deposits resting on the bed-rock, because of their high specific gravity, and. have been derived from the destruction of the rocks in which they 'originally occurred either, in quartzose veins or as disseminated particles. Tinstone occurs also in this way (" stream-tin "), and in Ceylon, Burma, Brazil, South Africa, &c., precious stones such as the diamond, ruby, spinel, chrysoberyl and tourmaline are found in beds of sand and gravel (gem sands).

In general the sand grains have a rounded or oviform shape due to mutual attrition during transport. Those which have been carried farthest are most rounded; sands deposited at no great distance from their parent rock often consist largely of angular grains. The smaller fragments may be carried along in suspension in water, and may travel for many miles without being sensibly worn; but coarse sands and fine gravels are swept along the bottom and are subjected to an intense grinding action. Something depends also on the hardness of the minerals present in the sands, yet even the diamonds and other gems found in sand deposits have often their corners worn and smoothed. Minerals with very perfect cleavage, such as mica, split up into thin plates under the shock of. impact with adjacent grains, and are never rounded like quartz or tourmaline. In deserts the transport of the sands is effected by the wind, and owing to the low viscosity of air even the smallest grains are not held in suspension but are rolled along the ground; hence very fine quartzose sands are sometimes met with in arid regions with every particle smoothed and polished. These sands flow almost .like a liquid and are used in hour-glasses. Similar desert sands " occur among the sandstones of the Trias and were doubtless formed in the manner described.

In addition to river sands, shore sands, marine sand deposits and desert sands, there are many other types of sand deposits. Blown sands are usually found near the seashore, but occur also at the margin of some great lakes like those of N. America; desert sands belong in great part to this category. These sands have been blown into their present position by the wind, and unless fixed by vegetation are constantly though slowly in movement, being in consequence a menace to agricultural land on their leeward sides. They may be shell sands, quartz sands or mixed sands, and often show very marked oblique stratification or " current bedding." The surface of blown sand deposits is generally marked by dunes. Glacial sands are common in districts like Britain and those parts of N. America which have been covered by an ice-sheet. They are really water-borne and have been deposited by streams, though they occur in situations where rivers no longer flow. The waters produced by the melting of the ice-sheets flooded extensive tracts of country, laying down sand and mud deposits in temporary lakes. These sands are usually angular, because they have not been transported to any great distance. The old high-level terraces which border the lower courses of many rivers, though usually consisting of gravel, are often accom p anied by considerable sand deposits.

Many of the Tertiary and some of the Secondary sandstone rocks are so incompletely consolidated by cementation that they are essentially sand rocks, and especially when weathered may be used as sources of sand. Thus in Britain there are Pliocene sands (St Erth, Cornwall, &c.), Eocene sands (Bagshot sands and Thanet sands); and the Lower and Upper Greensand (Cretaceous) are often dug in pits, though sometimes firmly coherent and more properly described as sandstones (q.v.).

The economic uses of sands are very numerous. They are largely employed for polishing and scouring both for domestic and manufacturing purposes. " Bath bricks " are made from the sand of the river Parrett near Bridgwater. Sand for glass-making was formerly obtained at Alum Bay in the Isle of Wight and at Lynn in Norfolk, but must be very pure for the best kinds of glass, and crushed quartz or flint is often preferred on this account. One of the principal uses of sand is for making mortar and cement: for this any good clean quartzose sand free from salts is suitable; it may be washed to remove impurities and sifted to secure uniformity in the size of the individual grains. Moulding sands, adapted for foundry purposes, generally contain a small admixture of clay. Sands are also employed in brick-making, in filtering, and for etching glass and other substances by means of the sand blast. (J. S. F.)


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Wiktionary

Up to date as of January 14, 2010

Definition from Wiktionary, a free dictionary

See also sand

Contents

German

Etymology

Old High German sant

Noun

Sand m. (genitive Sands or Sandes, plural Sande or Sände)

  1. sand (particles of rock)

Derived terms


Simple English

Sand is made of very small pieces of different rocks or minerals. When most of the pieces are at least two millimeters wide, it is called gravel. When most of the pieces are less than one-sixteenth of a millimeter wide (about as wide as the lines on a ruler), it is called silt.

Sand can be mixed with water to make concrete, a tough material which can be used to build buildings. It can also be used to make bricks or sand castles. When mixed with water sand will become mud.

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