Concretions


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Concretions

 

mineral formations of spherical shape found in sedimentary rock or recent sediments. Grains of minerals, rock debris, shells, fish teeth and bones, and plant remains may serve as centers of concretion. Most prevalent among the diverse forms of concretions are globular shapes and, less frequently, elliptical, disklike, and irregular (grown-together) shapes. In terms of structure, the most common are concentrically layered (conchoidal), coarse-banded, radiate-fibrous (spherulitic), and globular concretions. They usually consist of calcium carbonates (calcite and, less frequently, aragonite), ferric oxides and iron sulfides, calcium phosphates, gypsum, and manganese compounds. In limestone they frequently consist of silicic acid (flint nodules).

Concretions are found in deposits of various geologic systems and in sediments of modern lakes, seas, and oceans. Considerable accumulations of ferromanganese concretions (nearly 10 percent of the entire area of the ocean floor), which are of practical interest, are located on the surface of the floors of the Pacific, Atlantic, and Indian oceans.

References in periodicals archive ?
By induction hypothesis, there is an abstraction A with the properties stated in part 4 (corresponding to F), and there is a concretion B with the properties stated in part 3 (corresponding to C).
plebeius, calcium concretions in the form of blisters or loose pearls were only seen in older clam specimens, and seem to affect a reduced number of adult bivalves.
Mineral concretions such as the blueberries can be valuable indicators of sedimentary processes, environmental conditions, and ancient climates, says David C.
Gallaher RN, Perkins HF, Tan KH, Radcliffe D (1973b) Soil concretions.
The concretions vary between single spheruliths and compound spheruliths in the 8-mm-long adult storage organs.
One working hypothesis, out of several, is that the new-found spherules are also concretions but with a different composition.
c] productivity of oil shale and concretions in mass.
While the formation of granulation tissue is a well-known complication, (5) the development of fibrinous peritubular concretions on long-term tubes and the subsequent formation of an airway foreign body during removal have not been well documented, possibly because metal tubes are much less used.
The treatment of large bezoars and concretions is essentially surgical.
Secondary carbonates in horizon Ck have the form of pseudomycelia and hard hollow concretions.
Kidney concretions, located inside kidney tubules with varied sizes and shapes, were observed in 12 specimens.
The latter suggestion is supported by the work of Taylor and Schwertmann (1974a, 1974b), who found highly magnetic concretions in a wide range of Australian soils.