Geochemical and Pedochemical Weathering

Abstract

If a soild rock is broken down into a mass of rock fragments, the process is known as physical weathering (Chapter 7) and little change in the minerals of the rock takes place. In chemical weathering, however, the chemical elements in minerals (and therefore in rocks) are redistributed to a greater or lesser extent depending on the variables of weathering discussed in Section 2–3, and on the steady state discussed in Section 2–4. Chemical weathering of the outermost part of the lithosphere takes place in two stages; the first stage is the production of rotten rocks or saprolites, on which the second stage, soil formation, takes place. The first stage is geochemical weathering, and is mostly the inorganic alteration of solid rocks, but in the second stage the effects of vegetation, both living and dead, together with the effects of metabolism of microorganisms living in the geochemically altered rock material, are added to the continued inorganic processes, and this combination produces a soil which is the culmination of weathering at that particular locality.