ABSTRACT

The interaction of rock materials with rainwater occurs throughout the alteration column, from the abiotic water–rock interaction zone up to the soil zone of organic and mineral interaction. Soil clay minerals are for the most part an inheritance of water–rock clays formed at some depth in the profile which have been affected by changing chemical conditions as they interact with the organic matter and plant-controlled chemistry of the surface. The chemistry of surface alteration can be identified with the interaction between rainwater and solids. The relative importance of each type of chemical force in the alteration process on alterations occurring in a rock will depend on the chemistry and physical state of the rock involved. As the rainwater descends into the alteration sequence, it contains more dissolved ions and will have less effect on the products of incongruent dissolution, which are essentially the clay minerals.