The Clay Minerals in Soils

Abstract

Publisher Summary This chapter discusses the crystal structure, configuration, and functions of clay minerals. Clay mineralogy and clay physicochemistry have been developed almost entirely during the past decades. Clay mineral crystals are reactive crystalline solids. They are extremely flexible, flimsy, and fragile. The reactions of clay minerals are determined by the amount and nature of their external, internal, and voided surfaces. Clays are most commonly composed of the mixtures of one or more of the clay minerals with free oxides of silicon and free sesquioxides. Much of the material in these mixtures is composed of crystalline particles too small to be observed by the best optical microscope. Such mixtures are difficult to analyze. The methods used in the identification and estimation of the clay minerals include chemical, optical, thermal dehydration, electron microscopic, and X-ray diffraction. Clay minerals possess extremely large surface areas. These surfaces provide soils with vast capacities to store sorbed water, organic compounds, and plant nutrient elements. The functioning of clay minerals as a reservoir for water and available plant nutrient elements and the functioning of these minerals in the intricate reactions involved in water–nutrient–plant relationships are discussed in the chapter. All clay materials—through their binding action—provide anchorage for plant roots by holding the small masses of soil together in the form of structural aggregates.