Oolite


Oolite
Modern ooids from a beach on Joulter's Cay, The Bahamas
Ooids on the surface of a limestone; Carmel Formation (Middle Jurassic) of southern Utah
Thin-section of calcitic ooids from an oolite within the Carmel Formation (Middle Jurassic) of southern Utah

Oolite (egg stone) is a sedimentary rock formed from ooids, spherical grains composed of concentric layers. The name derives from the Hellenic word òoion for egg. Strictly, oolites consist of ooids of diameter 0.25–2 mm; rocks composed of ooids larger than 2 mm are called pisolites. The term oolith can refer to oolite or individual ooids.

Contents

Composition

Ooids are most commonly composed of calcium carbonate (calcite or aragonite), but can be composed of phosphate, chert, dolomite or iron minerals, including hematite. Dolomitic and chert ooids are most likely the result of the replacement of the original texture in limestone. Oolitic hematite occurs at Red Mountain near Birmingham, Alabama, along with oolitic limestone.

They are usually formed in warm, supersaturated, shallow, highly agitated marine water intertidal environments,though some are formed in inland lakes. The mechanism of formation starts with a small fragment of sediment acting as a 'seed' ,e.g. a piece of a shell. Strong intertidal currents wash the 'seeds' around on the seabed where they accumulate layers of chemically precipitated calcite from the supersaturated water.The oolites are commonly found in large current bedding structures that resemble sanddunes. The size of the oolite reflects the time they have had exposed to the water before they were covered with later sediment.

Oolites are often used in the home aquarium industry because their small grain size (0.2 to 1.22 mm) is ideal for shallow static beds and bottom covering of up to 1" in depth. Also known as "oolitic" sand, the sugar-sized round grains of this sand pass easily through the gills of gobies and other sand-sifting organisms. Importantly, this incredibly smooth sand promotes the growth of bacteria, which are important biofilters in home aquaria. Because of its extremely small grain size, oolitic sand has a lot of surface area, which promotes high bacterial growth.

Occurrence

Some exemplar oolitic limestone, a common term for an oolite, was formed in England during the Jurassic period, and forms the Cotswold Hills, the Isle of Portland with its famous Portland Stone,[1] and part of the North Yorkshire Moors. A particular type, Bath Stone, gives the buildings of the World Heritage City of Bath their distinctive appearance.

The islands of the Lower Keys in the Florida Keys, as well as some barrier islands east of Miami bordering Biscayne Bay, are mainly oolitic limestone, which was formed by deposition when shallow seas covered the area between periods of glaciation. The material consolidated and eroded during later exposure above the ocean surface.

One of the world's largest freshwater lakebed oolites is the Shoofly Oolite, a section of the Glenns Ferry Formation on southwestern Idaho's Snake River Plain. 10 million years ago, the Plain formed the bed of Lake Idaho. Wave action in the lake washed sediments back and forth in the shallows on the southwestern shore, forming ooids and depositing them on steeper benches near the shore in 2- to 40-feet thicknesses. When the lake drained (2 to 4 million years ago), the oolite was left behind, along with siltstone, volcanic tuffs and alluvium from adjacent mountain slopes. The other sediments eroded away, while the more resistant oolite weathered into hummocks, small arches and other intriguing natural "sculptures." The Shoofly Oolite lies on public land west of Bruneau, Idaho managed by the Bureau of Land Management (BLM). The physical and chemical properties of the Shoofly Oolite are the setting for a suite of rare plants, which the BLM protects through land use management and on-site interpretation.

This type of limestone is also found in Indiana in the United States. The town of Oolitic, Indiana, was founded for the trade of limestone and bears its name. Quarries in Oolitic, Bedford, and Bloomington contributed the materials for such iconic U.S. landmarks as the Empire State Building in New York and the Pentagon in Arlington, Virginia. Many of the buildings on the Indiana University campus in Bloomington are built with native oolitic limestone material, and the Soldiers' and Sailors' Monument in downtown Indianapolis, Indiana, is built mainly of grey oolitic limestone. The 1979 movie Breaking Away centers around the sons of quarry workers in Bloomington.

Oolites also appear in the Conococheague limestone, of Cambrian age, in the Great Appalachian Valley in Pennsylvania, Maryland, West Virginia, and Virginia.

Roggenstein is a term describing a specific type of oolite in which the cementing matter is argillaceous.

See also

References

  1. ^ Atkinson, Richard; Atkinson, Frances (1992) [1979]. Rocks & Minerals. The Observer's Book of. London: Bloomsbury. pp. 161–162. ISBN 1-8547-1044-3. "Oolitic limestones ... are among the most popular building stones and include Portland stone and Bath stone" 

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  • Oolite — Logo (von Webpage) …   Deutsch Wikipedia

  • Oolite — Скриншот из версии для Mac OS X …   Википедия

  • Oolite — O [ o]*lite, n. [Gr. w, o n an egg + lite: cf. F. o[ o]lithe. So named from its resemblance to the roe of fish.] (Geol.) A variety of limestone, consisting of small round grains, resembling the roe of a fish. It sometimes constitutes extensive… …   The Collaborative International Dictionary of English

  • oolite — (n.) rock consisting of fine grains of carbonate of lime, 1785, from Mod.L. oolites, from oo , comb. form of Gk. oon egg (cognate with O.E. æg, see EGG (Cf. egg) (n.)) + lithos stone. So called because the rock resembles the roe of fish …   Etymology dictionary

  • oolite — [ō′ōlith, ō′əlithō′ō līt΄, ō′əlīt΄] n. [Fr oölithe: see OO & LITE] 1. a tiny, spherical or ellipsoid particle with concentric layers, usually of calcium carbonate, formed in wave agitated sea waters 2. a rock composed chiefly of oolites: Also… …   English World dictionary

  • oolite — oolitic /oh euh lit ik/, adj. /oh euh luyt /, n. Geol. a limestone composed of minute rounded concretions resembling fish roe, in some places altered to ironstone by replacement with iron oxide. Also called egg stone. [1775 85; ( < F oölithe) <… …   Universalium

  • oolite — oolithe [ ɔɔlit ] n. f. ou m. VAR. oolite • 1752 n. f.; de oo et lithe ♦ Minér. Calcaire formé de grains sphériques (comparés à des œufs de poissons). Les oolithes sont caractéristiques du jurassique ancien. Formation analogue de grains d oxyde… …   Encyclopédie Universelle

  • Oolite — Oolithe Oolithes ferrugineuses …   Wikipédia en Français

  • oolite — /ˈoʊəlaɪt/ (say ohuhluyt) noun 1. a small spherical to ellipsoidal concretion, usually calcareous, formed in shallow water under special conditions. 2. a limestone composed of such concretions, in some places altered to ironstone by replacement… …   Australian English dictionary

  • oolite — oolitinė klintis statusas T sritis chemija apibrėžtis Klintis, susidedanti iš mažų apvalių kalcito grūdelių. atitikmenys: angl. oolite; oolitic limestone rus. оолитовый известняк …   Chemijos terminų aiškinamasis žodynas


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