Allophane and imogolite

Allophane and imogolite are poorly crystalline aluminosilicates characterized by small particle size, high specific surface area, and variable and/or permanent charge. Their high specific surface, unusual surface charge characteristics, and unique morphology lead to physical and chemical properties that can profoundly affect soil behavior. This chapter considers the environmental conditions under which these minerals form, their structural and surface characteristics, their effect on soil behavior, and their potential for beneficial use. Allophane and imogolite are responsible for the unique properties of soils derived from volcanic materials. Chemical composition is relatively stable in imogolite, but extremely variable in allophane, which may contain significant amounts of Fe in addition to Al and Si. The formation of allophane and imogolite is favored kinetically when dissolved Al and silica concentrations are between 0.1 and 4 mM.