An understanding of clay mineral structure and properties from basic to advanced

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Relative to the known practice of assessing the material performance from chemical behavior, the physical characteristics of clays are more important in defining various groups of clays. Clay particles can absorb or lose water in response to simple humiditycontent changes in the surrounding environment; when water is absorbed, it fills the spaces between the stacked silicates layers.[12] The specific gravity of any type of clay is, therefore, highly variable, resulting from the loss or gain of water. Most of the known clay types are rarely found separately in nature and are usually mixed with other types of microscopic crystals, including carbonates, feldspars, micas, and quartz. The structure of clay particles is perceived in layers; each layer is composed of two types of structural sheets: octahedral and tetrahedral. The tetrahedral sheet is composed of silicon-oxygen tetrahedra linked to neighboring tetrahedra by sharing three corners, resulting in a hexagonal network.[8] The remaining fourth corner of each tetrahedron forms a part to adjacent octahedral sheet. The octahedral sheet is usually composed of aluminum or magnesium in six-fold coordination with oxygen from the tetrahedral sheet and with hydroxyl. The two sheets together form a layer, and several layers may be joined in a clay crystallite by interlayer cations, Vander Waals force, electrostatic force, or by hydrogen bonding.

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