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Sand

Sand

Sand is any material composed of loose, stony grains between 1/16 mm and 2 mm in diameter. Larger particles are categorized as gravel, smaller particles are categorized as silt or clay . Sands are usually created by the breakdown of rocks, and are transported by wind and water , before depositing to form soils, beaches, dunes , and underwater fans or deltas. Deposits of sand are often cemented together over time to form sandstones.

The most common sand-forming process is weathering , especially of granite . Granite consists of distinct crystals of quartz, feldspar , and other minerals . When exposed to water, some of these minerals (e.g., feldspar) decay chemically faster than others (especially quartz), allowing the granite to crumble into fragments. Sand formed by weathering is termed epiclastic.

Where fragmentation is rapid, granite crumbles before its feldspar has fully decayed and the resulting sand contains more feldspar. If fragmentation is slow, the resulting sand contains less feldspar. Fragmentation of rock is enhanced by exposure to fast-running water, so steep mountains are often source areas for feldspar-rich sands and gentler terrains are often source areas for feldspar-poor sands. Epiclastic sands and the sandstones formed from them thus record information about the environments that produce them. A sedimentologist can deduce the existence of whole mountain ranges long ago eroded, and of mountain-building episodes that occurred millions of years ago from sandstones rich in relatively unstable minerals like feldspar.

The behavior of sand carried by flowing water can inscribe even more detailed information about the environment in sand deposits. When water is flowing rapidly over a horizontal surface, any sudden vertical drop in that surface splits the current into two layers, (1) an upper layer that continues to flow downstream and (2) a slower backflow that curls under in the lee of the dropoff. Suspended sand tends to settle out in the backflow zone, building a slope called a "slip face" that tilts downhill from the dropoff. The backflow zone adds continually to the slip face, growing it downstream, and as the slip face grows downstream its top edge continues to create a backflow zone. The result is the deposition of a lengthening bed of sand. Typically, periodic avalanches of large grains down the slip face (or other processes) coat it with thin layers of distinctive material. These closely-spaced laminations are called "crossbedding" because they angle across the main bed. Cross-bedding in sandstone records the direction of the current that deposited the bed, enabling geologists to map currents that flowed millions of years ago (paleocurrents).

Evidence of grain size, bed thickness, and cross-bedding angle, allows geologists to determine how deep and fast a paleocurrent was, and thus how steep the land was over which it flowed.

Ripples and dunesprobably the most familiar forms created by wind- or waterborne sandinvolve similar processes. However, ripples and dunes are more typical of flow systems to which little or no sand is being added. The downstream slip faces of ripples and dunes are built from grains plucked from their upstream sides, so these structures can migrate without growing. When water or wind entering the system (e.g., water descending rapidly from a mountainous region) imports large quantities of sand, the result is net deposition rather than the mere migration of sandforms.

Grain shape, too, records history. All epiclastic grains of sand start out angular and become more rounded as they are polished by abrasion during transport by wind or water. Quartz grains, however, resist wear. One trip down a river is not enough to thoroughly round an angular grain of quartz; even a long sojourn on a beach, where grains are repeatedly tumbled by waves, does not suffice. The well-rounded state of many quartz sands can be accounted for only by crustal recycling. Quartz grains can survive many cycles of erosion , burial, cementation into sandstone, uplift, and re-erosion. Recycling time is on the order of 200 million years, so a quartz grain first weathered from granite 2.4 billion years ago may have gone through 10 or 12 cycles of burial and re-erosion to reach its present day state. An individual quartz grain's degree of roundness is thus an index of its antiquity. Feldspar grains can also survive recycling, but not as well, so sand that has been recycled a few times consists mostly of quartz.

Sand can be formed not only by weathering but by explosive volcanism, the breaking up of shells by waves, the cementing into pellets of finer-grained materials (pelletization), and the precipitation of dissolved chemicals (e.g., calcium carbonate) from solution.

Pure quartz sands are mined to make glass and the extremely pure silicon employed in microchips and other electronic components.

See also Beach and shoreline dynamics; Bed or traction load; Bedding; Bedforms (ripples and dunes); Desert and desertification; Dune fields; Sedimentary rocks; Sedimentation

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sand

sand, rock material occurring in the form of loose, rounded or angular grains, varying in size from .06 mm to 2 mm in diameter, the particles being smaller than those of gravel and larger than those of silt or clay. Sand is formed as a result of the weathering and decomposition of igneous, sedimentary, or metamorphic rocks. Its most abundant mineral constituent is silica, usually in the form of quartz, and many deposits are composed almost exclusively of quartz grains. Many other minerals, however, are often present in small quantities, e.g., the amphiboles, the pyroxenes, olivine, glauconite, clay, the feldspars, the micas, iron compounds, zircon, garnet, tourmaline, titanite, corundum, and topaz. Some sands—e.g., coral sands, shell sands, and foraminiferal sands—are organic in origin. Sand grains may be rounded or more or less angular, and differences in shape and size account chiefly for differences in such important properties as porosity (proportion of interstices to the total mass), permeability to gases and liquids, and viscosity, or resistance to flow. Permeability and viscosity are also affected by the proportion of clayey matter present. The chief agents in accumulating sands into deposits are winds, rivers, waves, and glaciers; sand deposits are classified according to origin as fluviatile, lacustrine, glacial, marine, and eolian. The most extensive superficial deposits are seen in the desert and on beaches. The surface of a sand deposit may be level or very gently sloping, or the sand may be gathered by wind action into ridges called dunes. Sandstone and quartzite rocks are indurated masses of sand, and sand deposits are sometimes formed by the weathering of sandstone and quartzite formations. Sand is used extensively in the manufacture of bricks, mortar, cement, concrete, plasters, paving materials, and refractory materials. It is also used in the metallurgical industry, in the filtration of water, in pottery making, in glassmaking, in the manufacture of explosives, and as an abrasive. Other industrial uses are numerous. Although soils entirely composed of sand are too dry and too lacking in nourishment for the growth of plants, a soil that is to some extent sandy (a "light" soil) is favorable to certain types of agriculture and horticulture, as it permits the free movement of air in the soil, offers less resistance than a clay soil to growing roots, improves drainage, and increases ease of cultivation. Sand to which nutrient solutions have been added is often used in soilless gardening.

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sand

sand / sand/ • n. a loose granular substance, typically pale yellowish brown, resulting from the erosion of siliceous and other rocks and forming a major constituent of beaches, riverbeds, the seabed, and deserts. ∎  (sands) an expanse of sand, typically along a shore. ∎  a light yellow-brown color like that of sand. • v. [tr.] 1. smooth or polish with sandpaper or a mechanical sander: sand the rusty areas until you expose bare metal. 2. sprinkle or overlay with sand, to give better purchase on a surface. DERIVATIVES: sand·like / -ˌlīk/ adj.

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sand

sand often taken as a type of unstable or impermanent material.
built on sand lacking a firm foundation, ephemeral; often with biblical allusion to the parable in Matthew 7, in which of two houses it is the house built on rock which withstands the floods, and the house built on sand which falls.

See also bury one's head in the sand, (draw) a line in the sand, rope of sand, sands.

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sand

sand
1. In the commonly used Udden-Wentworth scale, particles between 62.5 and 2000 μm. Other classifications exist (see PARTICLE SIZE). In pedology, sand is defined as mineral particles of diameter 2.0–0.02 mm in the international system, and as 2.0–0.5 mm diameter particles in the USDA (American) system.

2. A class of soil texture.

3. See SHARP SAND.

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sand

sand
1. In rocks, according to the commonly used (Udden–Wentworth) scale, particles between 62.5 and 2000 μm.

2. In pedology, mineral particles of diameter 2–0.02 μm in the international system, or 2–0.05 μm in the USDA system.

3. A class of soil texture.

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sand

sand Mineral particles worn away from rocks by erosion, individually large enough to be distinguished with the naked eye. Sand is composed mostly of quartz, but black sand (containing volcanic rock) and coral sand also occur.

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sand

sand (pedol.)
1. Mineral particles of diameter 2–0.02 μm in the international system, or 2–0.05 μm in the USDA system.

2. A class of soil texture.

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"sand." A Dictionary of Plant Sciences. . Encyclopedia.com. 15 Oct. 2017 <http://www.encyclopedia.com>.

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sand

sand OE. sand = OS. sand, OHG. sant (Du. zand, G. sand), ON. sandr :- Gmc. *sandam, -az, rel. to Gr. hámathos, L. sabulum sand.
Hence sandy (-Y1) OE. sandiġ.

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"sand." The Concise Oxford Dictionary of English Etymology. . Encyclopedia.com. 15 Oct. 2017 <http://www.encyclopedia.com>.

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sand

sandand, band, bland, brand, expand, firsthand, gland, grand, hand, land, manned, misunderstand, offhand, rand, righthand, Samarkand, sand, stand, strand, thirdhand, underhand, undermanned, understand, unplanned, untanned, withstand •graduand • hatband • armband •headband • neckband • sweatband •waistband • waveband • wristband •broadband • showband • noseband •saraband • backhand • chargehand •farmhand • deckhand • stagehand •freehand • millhand • behindhand •longhand •beforehand, forehand •shorthand • gangland • Lapland •flatland • no-man's-land • Saarland •farmland • grassland • marshland •fenland • wetland • Sudetenland •wasteland • dreamland • peatland •Matabeleland • Ngamiland •fairyland • Dixieland • Swaziland •Thailand • Rhineland • swampland •washland • homeland • Heligoland •Basutoland •clubland, scrubland •timberland • borderland •wonderland • Nagaland • Helgoland •Bechuanaland, Gondwanaland •Mashonaland • Damaraland •Nyasaland • platteland • hinterland •fatherland • motherland •Namaqualand • Öland • allemande •confirmand • ordinand • Ferdinand •Talleyrand • firebrand • Krugerrand •honorand • Witwatersrand •greensand • quicksand • analysand •Streisand • ampersand •bandstand, grandstand, handstand •hatstand • kickstand • inkstand •washstand • hallstand • news-stand

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Sand

Sandaide-de-camp, aides-de-camp, anon, Asunción, au courant, begone, Bonn, bon vivant, Caen, Canton, Carcassonne, Ceylon, chaconne, chateaubriand, ci-devant, Colón, colon, Concepción, con (US conn), cretonne, don, Duchamp, Evonne, foregone, fromage blanc, Gabon, Garonne, gone, guenon, hereupon, Inchon, Jean, john, Jon, Le Mans, León, Luzon, Mont Blanc, Narbonne, odds-on, on, outgone, outshone, Perón, phon, piñon, Pinot Blanc, plafond, Ramón, Saigon, Saint-Saëns, Sand, Schwann, scone, shone, side-on, sine qua non, Sorbonne, spot-on, swan, thereon, thereupon, ton, Toulon, undergone, upon, Villon, wan, whereon, whereupon, won, wonton, yon, Yvonne •crayon, rayon •Leon, Lyons, neon, prion •Ceredigion • Mabinogion • nucleon •Amiens • dupion • parathion •Laocoon •gluon, Rouen •bon-bon • Audubon

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