oolite


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oolite

(ō`əlīt, ō`ō–), rock composed of small concretions, usually of calcium carbonate, containing a nucleus and clearly defined concentric shells. In the British Isles oolitic limestone is characteristic of the middle and upper Jurassic, which was formerly termed the Oolite on this account.

Oolite

 

(according to some sources, oolith), a spheroidal or ellipsoidal formation consisting of oxides and silicates of iron and manganese and of calcite, dolomite, aragonite, rhodochro-site, leptochlorite, and other minerals. Oolites range in size from several microns to 15–25 mm. Oolites larger than 2–5 mm are called pisolites. In the center of an oolite there is usually—but not always—a grain of sand or a fragment of the calcareous shell of some organism, around which thin layers of the precipitating substance accrete; as a result the structure of oolites is usually concentric-botryoidal. Oolites with radial and complex structures (combinations of concentric-botryoidal and radial structures) are also found. Oolites form in seawater and warm springs as a result of colloid-chemical and biochemical processes. Ferruginous oolites are a variety of iron ore.

REFERENCE

Shvetsov, M. S. Petrografiia osadochnykh porod, 3rd ed. Moscow, 1958.

V. A. GROSSGEIM

oolite

[′ō·ə‚līt]
(petrology)
A sedimentary rock, usually a limestone, composed principally of cemented ooliths. Also known as eggstone; roestone.

oolite

A granular limestone, each grain of which is more or less spherical and made up of concentric coats of carbonate of lime formed around a nucleus.

oolite

any sedimentary rock, esp limestone, consisting of tiny spherical concentric grains within a fine matrix
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