Amorphous Clay Constituents of Soils

Abstract

This chapter discusses recent progress in studies of the amorphous clay constituents of soils during the past ten years and focuses on their nature, properties, and genesis. Effort is made to collect analytical data on natural clay systems, although they often have been inconclusive and to indicate similarities and differences between different kinds of amorphous clay materials. The amorphous clay constituents in soils derived from volcanic ash have been studied most extensively and intensively because they are predominating in the clay fraction and have predominating influence on the physical and chemical properties of the soils. Considerable progress has been made in characterization of amorphous clay constituents such as allophane, imogolite, and opaline silica, by application of selective dissolution techniques combined with physical methods as represented by infrared spectroscopy and electron microscopy. A better understanding of the processes of soil development from volcanic ash has been obtained by applying advanced methods of mineralogical analysis and by relating the formation and transformation of the amorphous clay constituents to crystalline clay constituents and to accumulation of organic matter.