Sandstone

Sandstone is a sedimentary rock composed mainly of sand-size mineral 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 the north of England, have been found less resistant, necessitating repair and replacement in older buildings. [ [http://www.sci-eng.mmu.ac.uk/manchester_stone/images.asp?page1=2&vartype=building&id=&offset=0# Edensor, T. & Drew, I. "Building stone in the City of Manchester: St Ann's Church"] ] 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 sandstone usually allow percolation of water and are porous enough to store large quantities, making them valuable aquifers. 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 limestones or other rocks fractured by seismic activity.

Origins of Sandstone

Sandstones are "clastic" in origin (as opposed to "organic", like chalk and coal, or "chemical", like gypsum and jasper). 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 in the range of 0.1 mm to 2 mm (clays and rocks with smaller grain sizes including siltstones and shales are typically called "argillaceous" sediments; rocks with larger grain sizes including breccias and conglomerates are termed "rudaceous" sediments).

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 sand dune region). 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 (terra cotta), 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
# Rivers (levees, point bars, channel sands)
# Alluvial fans
# Glacial outwash
# Lakes
# Deserts (sand dunes and ergs)

* Marine environments
# Deltas
# Beach and shoreface sands
# Tidal flats
# Offshore bars and sand waves
# Storm deposits (tempestites)
# Turbidites (submarine channels and fans)

Types of sandstone

Once the geological characteristics of a sandstone have been established, it can then be assigned to one of three broad groups:
* arkose or "arkosic" sandstones, which have a high (>25%) feldspar content and a composition similar to granite.
* "quartzose" sandstones, also known as "beach sand", which have a high (>90%) quartz content. Sometimes these sandstones are termed "orthoquartzites", e.g., the Tuscarora Quartzite of the Ridge-and-valley Appalachians.
* "argillaceous" sandstones, such as greywacke or bluestone, which have a significant clay or silt content.

Aeolian sandstone 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.

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.

Notes

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, [http://www.lib.utexas.edu/geo/folkready/folkprefrev.html "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
* [http://minerals.usgs.gov/minerals/pubs/commodity/stone_dimension/dstonmyb05.pdf USGS Minerals Yearbook: Stone, Dimension]

Gallery

See also

* Bargate stone
* Beaver river sandstone
* Brownstone
* Dimension stone
* Geology
* Hummelstown brownstone
* List of minerals
* List of stone
* Old Red Sandstone
* New Red Sandstone
* Sarsen
* Sedimentary basins
* Yorkstone
* Wisconsin Dells
* Uluru