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Sandstone
 —  Sedimentary Rock  —
Sandstone Image
Prepared sample of sandstone
Composition
Typically quartz and/or feldspar (on earth); lithic fragments are also common. Other minerals may be found in particularly immature sandstone.

Sandstone (sometimes known as arenite) is a sedimentary rock composed mainly of sand-sized minerals or rock grains. Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any color, but the most common colors are tan, brown, yellow, red, gray and white. Since sandstone beds often form highly visible cliffs and other topographic features, certain colors of sandstone have been strongly identified with certain regions.

Some sandstones are resistant to weathering, yet are easy to work. This makes sandstone a common building and paving material. However, some that have been used in the past, such as the Collyhurst sandstone used in North West England, have been found less resistant, necessitating repair and replacement in older buildings.[1] Because of the hardness of the individual grains, uniformity of grain size and friability of their structure, some types of sandstone are excellent materials from which to make grindstones, for sharpening blades and other implements. Non-friable sandstone can be used to make grindstones for grinding grain, e.g., gritstone.

Rock formations that are primarily composed of sandstone usually allow percolation of water and other fluids and are porous enough to store large quantities, making them valuable aquifers and petroleum reservoirs. Fine-grained aquifers, such as sandstones, are more apt to filter out pollutants from the surface than are rocks with cracks and crevices, such as limestone or other rocks fractured by seismic activity.

Contents

Origins

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.
Millet-Seed sandstone macro (size: ~4 cm or ~1.6 in).

Sandstones are clastic in origin (as opposed to either organic, like chalk and coal, or chemical, like gypsum and jasper).[2] They are formed from cemented grains that may either be fragments of a pre-existing rock or be mono-minerallic crystals. The cements binding these grains together are typically calcite, clays and silica. Grain sizes in sands are defined (in geology) within the range of 0.0625 mm to 2 mm (0.002-0.079 inches). Clays and sediments with smaller grain sizes not visible with the naked eye, including siltstones and shales, are typically called argillaceous sediments; rocks with larger grain sizes, including breccias and conglomerates are termed rudaceous sediments.

Red sandstone interior of Lower Antelope Canyon, Arizona, worn smooth by erosion from flash flooding over millions of years.

The formation of sandstone involves two principal stages. First, a layer or layers of sand accumulates as the result of sedimentation, either from water (as in a river, lake, or sea) or from air (as in a desert). Typically, sedimentation occurs by the sand settling out from suspension; i.e., ceasing to be rolled or bounced along the bottom of a body of water (e.g., seas or rivers) or ground surface (e.g., in a desert or erg). Finally, once it has accumulated, the sand becomes sandstone when it is compacted by pressure of overlying deposits and cemented by the precipitation of minerals within the pore spaces between sand grains.

The most common cementing materials are silica and calcium carbonate, which are often derived either from dissolution or from alteration of the sand after it was buried. Colors will usually be tan or yellow (from a blend of the clear quartz with the dark amber feldspar content of the sand). A predominant additional colorant in the southwestern United States is iron oxide, which imparts reddish tints ranging from pink to dark red (terracotta), with additional manganese imparting a purplish hue. Red sandstones are also seen in the Southwest and West of England and Wales, as well as central Europe and Mongolia. The regularity of the latter favors use as a source for masonry, either as a primary building material or as a facing stone, over other construction.

The environment where it is deposited is crucial in determining the characteristics of the resulting sandstone, which, in finer detail, include its grain size, sorting and composition and, in more general detail, include the rock geometry and sedimentary structures. Principal environments of deposition may be split between terrestrial and marine, as illustrated by the following broad groupings:

  • Terrestrial environments
Sandstone near Stadtroda, Germany.
  1. Rivers (levees, point bars, channel sands)
  2. Alluvial fans
  3. Glacial outwash
  4. Lakes
  5. Deserts (sand dunes and ergs)
  • Marine environments
  1. Deltas
  2. Beach and shoreface sands
  3. Tidal flats
  4. Offshore bars and sand waves
  5. Storm deposits (tempestites)
  6. Turbidites (submarine channels and fans)

Types

Sandstone composed mainly of quartz grains

Sandstones fall into several major groups based on their mineralogy and texture. Below is a partial list of common sandstone types.

  • quartz arenites are made up almost entirely of quartz grains, usually well sorted and rounded. These pure quartz sands result from extensive weathering that occurred before and during transport and removed everything but quartz, the most stable mineral. They are common in beach environments.
  • arkoses are more than 25 percent feldspar.[2] The grains tend to be poorly rounded and less well sorted than those of pure quartz sandstones. These feldspar-rich sandstones come from rapidly eroding granitic and metamorphic terrains where chemical weathering is subordinate to physical weathering.
  • lithic sandstones contain many lithic fragments derived from fine-grained rocks, mostly shales, volcanic rocks, and fine-grained metamorphic rocks.
  • graywacke is a heterogeneous mixture of lithic fragments and angular grains of quartz and feldspar, and/or grains surrounded by a fine-grained clay matrix. Much of this matrix is formed by relatively soft fragments, such as shale and some volcanic rocks, that are chemically altered and physically compacted after deep burial of the sandstone formation.
  • Eolianite is a term used for a rock which is composed of sand grains that show signs of significant transportation by wind. These have usually been deposited in desert environments. They are commonly extremely well sorted and rich in quartz.
  • Oolite is more a limestone than a sandstone, but is made sand-sized carbonate ooids, and is common in saline beaches with gentle wave action.

Sandstone composition is (generally) based on the make up of the framework, or sand-sized grains in the sandstone. This is typically done by point-counting a thin section of the sandstone using a method like the Gazzi-Dickinson Method. The composition of a sandstone can have important information regarding the genesis of the sediment when used with QFL diagrams.


According to the USGS, U.S. sandstone production in 2005 was 192,000 metric tons worth $24.3 million, the largest component of which was the 121,000 metric tons worth $9.75 million of flagstone or dimension stone.[3]

Gallery

See also

Notes

  1. ^ Edensor, T. & Drew, I. Building stone in the City of Manchester: St Ann's Church
  2. ^ a b "A Basic Sedimentary Rock Classification", L.S. Fichter, Department of Geology/Environmental Science, James Madison University (JMU), Harrisonburg, Virginia, October 2000, webpage: JMU-sed-classif (accessed: March 2009): separates clastic, chemical & biochemical (organic).
  3. ^ USGS 2005 Minerals Yearbook (see below: References).

References

  • Boggs, J.R., 2000, Principles of sedimentology and stratigraphy, 3rd ed. Toronto: Merril Publishing Company. ISBN 0-13-099696-3.
  • Folk, R.L., 1965, Petrology of sedimentary rocks PDF version. Austin: Hemphill’s Bookstore. 2nd ed. 1981, ISBN 0-914696-14-9.
  • Pettijohn, F.J., P.E. Potter and R. Siever, 1987, Sand and sandstone, 2nd ed. Springer-Verlag. ISBN 0-387-96350-2.
  • Scholle, P.A., 1978, A Color illustrated guide to constituents, textures, cements, and porosities of sandstones and associated rocks, American Association of Petroleum Geologists Memoir no. 28. ISBN 0-89181-304-7.
  • Scholle, P.A., and D. Spearing, 1982, Sandstone depositional environments: clastic terrigenous sediments , American Association of Petroleum Geologists Memoir no. 31. ISBN 0-89181-307-1.
  • USGS Minerals Yearbook: Stone, Dimension, Thomas P. Dolley, U.S. Dept. of the Interior, 2005 (format: PDF).

1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

SANDSTONE, in petrology, a consolidated sand rock built up of sand grains held together by a cementing substance. The size of the particles varies within wide limits and in the same rock may be uniform or irregular: the coarser sandstones are called grits, and form a transition to conglomerates (q.v.), while the finer grained usually contain an admixture of mud or clay and pass over by all stages into arenaceous shales and clay rocks. Greywackes (q.v.) are sandstones belonging to the older geological systems, such as the Silurian or Cambrian, usually of brown or grey colour and very impure.

The minerals of sandstones are the same as those of sands. Quartz is the commonest; with it often occurs a considerable amount of felspar, and usually also some white mica. Chlorite, argillaceous matter, calcite and iron oxides, are exceedingly common in sandstones, and in some varieties are important constituents; garnet, tourmaline, zircon, epidote, rutile and anatase are often present though rarely in any quantity. According to their composition we may distinguish siliceous sandstones (some of these are so pure that they contain 99% of silica, e.g. Craigleith stone and some gannisters), felspathic sandstones or arkoses (less durable and softer than the siliceous sandstones); micaceous sandstones, with flakes of mica lying along the bedding planes; argillaceous sandstones; ferruginous sandstones, brown or red in colour with the sand grains coated with red haematite or brownish yellow limonite; impure sandstones, usually in the main consisting of quartz with a large addition of other minerals.

The cementing material is often fine chalcedonic silica, and exists in such small quantity that it is difficult to recognize even with the microscope. In some of the cherty sandstones of the Greensand the chalcedonic cement is much more abundant: these rocks also contain rounded grains of glauconite, to which they owe their green colour. Crystalline silica (quartz) is deposited interstitially in some sandstones, often in regular parallel crystalline growth on the original sand grains, and when there are cavities or fissures in the rock may show the development of regular crystalline facets. By this process the rock becomes firmly compacted, and is then described as a quartzite. A calcareous cement is almost equally common: it may be derived from particles of shells or other calcareous fossils originally mixed with the sand and subsequently dissolved and redeposited in the spaces between the other grains. In Fontainebleau sandstone and some British Secondary rocks the calcite is in large crystalline masses, which when broken show plane cleavages mottled with small rounded sand grains; in the French rock external rhombohedral faces are present and the crystals may be of considerable size. Many of the British Jurassic and Cretaceous sandstones (e.g. Kentish Rag, Spilsby Sandstone) are of this calcareous type. In ferruginous sandstones the iron oxides usually form only a thin pellicle coating each grain, but sometimes, in the greensands, are more abundant, especially in concretionary masses or segregations. In argillaceous sandstones the fine clayey material, compacted by pressure, holds the sand grains together, and rocks of this kind are soft and break up easily when exposed to the weather or submitted to crushing tests. Among other cementing materials may be mentioned, dolomite, barytes, fluorite and phosphate of lime, but these are only locally found.

Many sandstones contain concretions which may be several feet in diameter, and are sometimes set free by weathering or when the rock is split open by a blow. Most frequently these are siliceous, and then they interfere with the employment of the rock for certain purposes, as for making grindstones or for buildings of fine dressed stone. Argillaceous concretions or clay galls are almost equally common, and nodules of pyrites or marcasite; the latter weather to a brown rusty powder, and are most undesirable in building stones. Phosphatic, ferruginous, barytic and calcareous concretions occur also in some of the rocks of this group. We may also mention the presence of lead ores (the Eifel, Germany), copper ores (Chessy and some British Triassic sandstones) and manganese oxides. In some districts (e.g. Alsace) bituminous sandstones occur, while in N. America many Devonian sandstones contain petroleum. Many Coal-Measures sandstones contain remains of plants preserved as black impressions.

The colours of sandstones arise mostly from their impurities; pure siliceous and calcareous sandstones are white, creamy or pale yellow (from small traces of iron oxides). Black colours are due to coal or manganese dioxide; red to haematite (rarely to copper oxide); yellow to limonite, green to glauconite. Those which contain clay, fragments of shale, &c., are often grey (e.g. the Pennant Grit of S. Wales).

Sandstones are very extensively worked, mostly by quarries but sometimes by mines, in all districts where they occur and are used for a large variety of purposes. Quarrying is facilitated by the presence of two systems of joints, developed approximately in equal perfection, nearly at right angles to one another and perpendicular to the bedding planes. Sometimes this jointing determines the weathering of the rock into square pillar-like forms or into mural scenery (e.g. the Quader Sandstein of Germany). As building stones sandstones are much in favour, especially in the Carboniferous districts of Britain, where they can readily be obtained. They have the advantage of being durable, strong and readily dressed. They are usually laid "on the bed," that is to say, with their bedding surfaces horizontal and their edges exposed. The finer kinds of sandstone are often sawn, not hewn or trimmed with chisels. Pure siliceous sandstones are the most durable, but are often very expensive to dress and are not obtainable in many places. Sandstones are also used for grindstones and for millstones. For engineering purposes, such as dams, piers, docks and bridges, crystalline rocks, such as granite, are often preferred as being obtainable in larger blocks and having a higher crushing strength. Very pure siliceous sandstones (such as the gannisters of the north of England) may be used for lining furnaces, hearths, &c. As sandstones are always porous, they do not take a good polish and are not used as ornamental stones, but this property makes them absorb large quantities of water, and consequently they are often important sources of water supply (e.g. the water-stones of the Trias of the English Midlands). Silver is found in beds of sandstone in Utah, lead near Kommern in Prussia, and copper at Chessy near Lyons. (J. S. F.)


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Simple English

File:Siccar Point red capstone
Siccar Point, eroded gently sloping Devonian Old Red Sandstone layers forming capping over conglomerate layer and older vertically bedded Silurian greywacke rocks.
File:Lower antelope 2
Red sandstone

Sandstone is a sedimentary rock, it is a rock made of compacted sand "glued" together with either calcium carbonate, quartz, or hematite. It is used for building large buildings in many countries. When sandstone is heated it turns black. It can be used to decorate a home. For example, paving slabs are made out of sandstone.








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