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 ?
We consider that emergence of Venus verrucosa, in response to unfavorable environmental conditions, is promoted by formation of biogenic concretions and infestation by some invertebrate species.
Instead, the team brought portable imaging machines to the warehouse where the concretions were stored and worked around the irregularly shaped objects.
Il s'agit de l'association recurrente "personnage masculin + signe ponctue [soleiforme]" dans une version tres proche de celle exprimee sur les concretions de l'entree de l'abri Gilles (Ardeche).
Characteristics of the 3 SQ groups in the watershed Soil type Characteristics Kooticha Black, very heavy, highly waterlogged, fertile, deep, wide cracks, located on flat land Abolse Very dark, heavy, fertile, water logged, deep, wide cracks, some carbonate concretions, located on gentle slope Carii Card Dark grey, slightly heavy, relatively shallow, weedy, cracking, more carbonate concretions, poor fertility, eroded Soil type Advantages Disadvantages Kooticha Less erosion, productive Drainage problem, difficult for tillage, heavy soil, higher fertiliser demand Abolse Productive, low fertiliser None demand, not difficult for tillage Carii No water logging, easy for High fertiliser demand, less tillage water-holding capacity, erosion Table 4.
After 9 months of exposure to various concentrations of chloroform, there were significant differences overall between males and females in their responses to chloroform for gallbladder concretions (f = 5.76; p = 0.0231), cystic duct hyperplasia (f = 4.94; p = 0.0341), and bile duct epithelium hyperplasia (f = 6.43, p = 0.0169).
assuming that [x.sub.1], ..., [x.sub.k] [is not an element of] fv(Q), and to concretions:
Odd-shaped crusty coverings or concretions are X-rayed first to discover what's inside.
Choosing "skin" as the location, users are offered 11 morphologic choices (macular, papular, vesicular, etc; Figure 2) with descriptions ("crusted, [sic] circumscribed, discolored, desiccated concretions") for the second selection.
Nevertheless, despite P.'s caution not to offer direct theological interpretations of physical theory, his easy juxtaposition of biblical, philosophical, and scientific ideas (as in his explanation of divine Spirit and angels as concretions of force fields) may cause discomfort in scientists as well as theologians.