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Definition of CLAY MINERAL
: any of a group of hydrous silicates of aluminum and sometimes other metals formed chiefly in weathering processes and occurring especially in clay and shale
First Known Use of CLAY MINERAL
Any of a group of important hydrous aluminum silicates with a layered structure and very small (less than 0.005 mm or microscopic) particle size. They are usually the products of weathering. Clay minerals occur widely in such sedimentary rocks as mudstones and shales, in marine sediments, and in soils. Different geologic environments produce different clay minerals from the same parent rock. They are used in the petroleum industry (as drilling muds and as catalysts in refining) and in the processing of vegetable and mineral oils (as decolorizing agents).