Oolite oroölite (from Ancient Greek ᾠόν (ōión) 'egg stone')[1] is asedimentary rock formed fromooids, spherical grains composed of concentric layers.[2] Strictly, oolites consist of ooids of diameter 0.25–2 millimetres;rocks composed of ooids larger than 2 mm are calledpisolites. The termoolith can refer to oolite or individual ooids.
Ooids are most commonly composed ofcalcium carbonate (calcite oraragonite), but can be composed of phosphate, clays,chert,dolomite oriron minerals, includinghematite. Dolomitic and chert ooids are most likely the result of the replacement of the original texture in limestone. Oolitic hematite occurs atRed Mountain nearBirmingham, 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', such as 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 largecurrent bedding structures that resemble sand dunes. The size of the oolites reflect the time that they were 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 ofgobies and other sand-sifting organisms. This unusually 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.
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Some exemplar ooliticlimestone was formed inEngland during theJurassic period, and forms theCotswold Hills, theIsle of Portland with its famousPortland Stone,[3] and part of theNorth York Moors. A particular type,Bath Stone, gives the buildings of theWorld Heritage City ofBath their distinctive appearance.CarboniferousHunts Bay Oolite lies under much of southWales.
TheMiami Rock Ridge of southeastern Florida, the islands of the LowerFlorida Keys, and much of theEverglades, are underlain byMiami Oolite.[4] This limestone was formed by deposition when shallow seas covered the area betweenperiods 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,[5] a section of the Glenns Ferry Formation on southwesternIdaho'sSnake River Plain. 10 million years ago, the Plain formed the bed ofLake Idaho. Wave action in the lake washed sediments back and forth in the shallows on the southwestern shore, formingooids and depositing them on steeper benches near the shore in 2- to 40-foot thicknesses. When the lake drained (2 to 4 million years ago), the oolite was left behind, along withsiltstone, volcanictuffs and alluvium from adjacent mountain slopes. The other sediments eroded away, while the more resistant oolite weathered into hummocks, small arches and other natural "sculptures". The Shoofly Oolite lies on public land west ofBruneau, Idaho managed by theBureau 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 inIndiana in theUnited States. The town ofOolitic, Indiana, was founded for the trade in limestone and bears its name. Quarries in Oolitic,Bedford, andBloomington contributed the materials for such U.S. landmarks as theEmpire State Building inNew York andthe Pentagon inArlington, Virginia. Many of the buildings on theIndiana University campus in Bloomington are built with native oolitic limestone material, and theSoldiers' and Sailors' Monument in downtownIndianapolis, Indiana, is built mainly of grey oolitic limestone.
Oolites also appear in theConococheague limestone, ofCambrian age, in theGreat Appalachian Valley inPennsylvania,Maryland,West Virginia, andVirginia.
Rogenstein is a term describing a specific type of oolite in which the cementing matter isargillaceous.
Oolitic limestones … are among the most popular building stones and include Portland stone and Bath stone
Media related toOolite at Wikimedia Commons
Ooids and oolite at Wikibooks