User:Sunshineasteraceae/sandbox

Structures of Clay Minerals in Soil
Clay minerals are layer silicates formed as products of chemical weathering of silicate minerals at the Earth's surface are form an important group of the phyllosilicates (sheet silicate) family of minerals distinguished by layered structures composed of sheets of silica tetrahedral linked to octrahedral sheets .The octrahedral sheet is comprised of oxygens and hydroxyls with aluminum, iron, and magnesium atoms arranged in an octahedral formation. The tetrahedral sheet is comprised of silica atoms equidistant from four oxygens (or hydroxyls) arranged to form a tetrahedron with silicon atom in the center. The tetrahedra are arranged in a hexagonal network repeated, to form the tetrahedral sheet. Tetrahedral sheets and octahedral sheets are joined through sharing of oxygens/hydroxyls to form 1:1 clay mineral layer or 2:1 clay mineral layer. The geochemical importance of clay minerals is related to their cosmopolitan presence in soils and sediments, high specific surface area, and ion exchange capacities.



Classification of clay minerals
Common clay minerals are classified according to layer type, magnitude of net layer charge, type of interlayer material, character of the octahedral sheet, and the composition or structure of the individual species.


 * Allophane
 * Kaolinite
 * Smectite
 * Vermiculite
 * Illite
 * Chlorite
 * Palygorskite and sepiolite
 * Mixed-layer clay minerals

Properties of clay minerals in soils
The small size and unique crystalline structures give clay minerals special properties including: cation exchange capabilities, plastic behavior when wet, catalytic abilities, swelling behavior, and low permeability.

Clay minerals can act as electron acceptors and/or donors in organic reactions and are important in understanding cation and ion exchange in soils, due to interlayer water cations and layer charge. Clay has absorptive capacity through physical absorption, ion exchange absorption, and zeolitic absoprtion. The permeability of clay minerals can be explained by the type and distribution of clay minerals within the pore system.