ABSTRACT
Heterogeneity is shown in the composition of minerals within a soil profile. Soil profiles comprise a lower portion and an upper portion. As for the ferromagnesian minerals, amphiboles, pyroxenes and olivines, the alteration of serpentines depends on extent of leaching, hence drainage, as well as to a degree on the composition of the originating serpentine. Feldspars can give rise to a wide variety of minerals on weathering, among them smectites, illites, gibbsite, quartz, and, most commonly, kaolinite and halloysite. Chlorites are also phyllosilicates and are subject to transformations as in micas, with the interlayer hydroxy species being prone to replacement by hydrated cations as with micas. One parameter, obvious from the descriptions of water–rock interactions, is the overall pH of the alteration system under consideration. Since hydrogen ions are the major vector of chemical displacement and change in silicate materials, pH will undoubtedly be primordial in the amount and rate of change.
