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Clay minerals in clays are most easily identified using X-ray diffraction rather than chemical or physical tests. [ 23 ] Varve (or varved clay ) is clay with visible annual layers that are formed by seasonal deposition of those layers and are marked by differences in erosion and organic content.
Clay cannot be resolved by optical microscopes as its particles are 0.002 mm (7.9 × 10 −5 in) or less in diameter and a thickness of only 10 angstroms (10 −10 m). [16] [17] In medium-textured soils, clay is often washed downward through the soil profile (a process called eluviation) and accumulates in the subsoil (a process called ...
The chemistry of clay, including its capacity to retain nutrient cations such as potassium and ammonium, is important to soil fertility. [7] Because the individual particles in clay are less than 4 micrometers (0.00016 in) in size, they cannot be characterized by ordinary optical or physical methods.
Kaolinite (/ ˈ k eɪ. ə l ə ˌ n aɪ t,-l ɪ-/ KAY-ə-lə-nyte, -lih-; also called kaolin) [5] [6] [7] is a clay mineral, with the chemical composition Al 2 Si 2 O 5 4.It is a layered silicate mineral, with one tetrahedral sheet of silica (SiO 4) linked through oxygen atoms to one octahedral sheet of alumina (AlO 6).
In soils, clay is a soil textural class and is defined in a physical sense as any mineral particle less than 2 μm (8 × 10 −5 in) in effective diameter. Many soil minerals, such as gypsum , carbonates, or quartz, are small enough to be classified as clay based on their physical size, but chemically they do not afford the same utility as do ...
Edge-of-clay oxygen atoms are not in balance ionically as the tetrahedral and octahedral structures are incomplete. [92] Hydroxyls may substitute for oxygens of the silica layers, a process called hydroxylation. When the hydrogens of the clay hydroxyls are ionised into solution, they leave the oxygen with a negative charge (anionic clays). [93]
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Soil texture is a classification instrument used both in the field and laboratory to determine soil classes based on their physical texture. Soil texture can be determined using qualitative methods such as texture by feel, and quantitative methods such as the hydrometer method based on Stokes' law.