clay mineral
clay mineral
A colloidal-size, crystalline, hydroxyl silicate having a crystal structure of the two-layer (7 Aa) type (kaolinite), or of the three-layer (14 Aa) type (smectite), in which layers of silicon and aluminum ions have tetrahedral coordination with respect to oxygen, while layers of aluminum, ferrous and ferric iron, magnesium, chromium, lithium, manganese, and other cations have octahedral coordination with respect to oxygen and to hydroxyl ions. Exchangeable cations may attach to the silicate layers in an amount determined by the excess negative charge within the composite layers. These cations commonly are calcium and sodium, but may also be potassium, magnesium, hydronium, aluminum, or others. The most common clay minerals belong to the kaolinite, smectite, attapulgite, and illite (hydromica) groups. Mixed-layer clay minerals are either randomly or regularly interstratified intergrowths of two or more clay minerals.
Any mineral found in the clay fraction (less than 4 mu m) of a soil or sediment; e.g., rock flour comminuted by glacial grinding.
Any kandite mineral of the kaolinite-serpentine group.
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