ABSTRACT
Soils in the hot – and often humid – zones can be regarded as zonal, where climate is the controlling factor, or intrazonal, where volcanic or other, for example, serpentitic parent materials are the overriding influence on the results of weathering. Of the various soil forming factors, climate is a central driving force in the alteration of rock minerals and the formation of clays. Zonal soils have well-formed horizons and are largely the effect of climatic and biological influences, rather than those from the parent materials. Though there have been innumerable studies of the clay mineralogy of individual soils or small sets of soils, only a few have attempted to give a nationwide summary of the types of clays occurring in soils. In Australia, the hot and generally humid north of the continent gives rise to soils in which kaolin is dominant, but illite can also appear, as well as iron oxides and sometimes also smectite.
