Concretions


Also found in: Dictionary, Thesaurus, Medical, Legal.

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 ?
The massive presence of iron mottles and concretions at this depth most likely supports this finding.
Though not nearly as titillating as a 20-million-year-old turtle, concretions are fairly fascinating phenomena by themselves.
Within the lower sand layer and the silt just above it, black concretions appear as very hard clusters of sand grains cemented in a star-burst pattern by a black mineral up to 3 centimeters in diameter (see Figure 3).
Other types of bezoars include trichobezoar, composed of hair, and lithobezoar, composed of hard concretions such as small stones or pebbles.
Benign ducts, in contrast, retain their epithelium and instead of cellular debris may contain plugs and concretions of secretions which, if calcified, become calculi (Figure 3, B).
Some concretions constantly are sprayed with water to preserve the artifacts within; others rest inside water tanks.
A walkway to the Gallery of Gems and Gold is lined with some of the ROM's largest and most impressive mineral specimens, among them a sandstone formation known colloquially as a gogotte--a bizarre natural structure formed from concretions in 30-million-year-old sands left by an ancient river system in France.
Associations can also be superficial because the roughness and nature of the shell allows the formation of resistant deposits of hard biogenic concretions (Fig.
These processes are revealed in many horizons by well expressed hydromorphic features, like Fe mottles, Fe-Mn concretions and gley colors (neutral greenish or bluish colors).
13) Kirby (12) suggests that Celsus (and subsequently Galen) saw cataract disease not as pathology of the lens, but as opaque aqueous concretions between the lens and iris; this view persisted through the Middle Ages.
Tasjo is a sedimentary uranium deposit where uranium mineralization is associated with concretions of carbonate-fluorapatite, which constitute up to 20% of the rock.