ABSTRACT
The solid phase of soil is composed of two distinct materials: inorganic and organic. Of these, the inorganic materials, or minerals, predominate in virtually all soils except Histosols. A mineral is defined as any naturally occurring inorganic substance. In the soil sciences, minerals are grouped into two idealized categories: crystalline and amorphous. Crystalline minerals are naturally occurring inorganic compounds composed of atoms arranged in a three-dimensional and periodic (repeating) pattern. Amorphous minerals are naturally occurring inorganic compounds that have no periodic three-dimensional arrangement of atoms. Minerals exert a pronounced influence on the chemistry of soil solutions. Through precipitation and dissolution (weathering), they regulate the chemical composition of the soil solution (see Chapter 6). Mineral surfaces are also inherently reactive, potentially forming strong or weak chemical bonds with soluble substances and further regulating the composition of the soil solution (see Chapters 7 and 8). A majority of the discussion of minerals in this chapter is devoted to the silicates, the most common class of minerals in the soil environment. Aside from their abundance, a subclass of the silicates, the phyllosilicates or clay minerals, have a substantial impact on the physical and chemical characteristics of soil. With few exceptions, the phyllosilicates and associated clay materials exert the greatest impact on the fate and behavior of substances in the soil environment.
