Abstract
A study of the clay mineralogy of a number of soils from West Africa and South America has enabled the construction of a generalized weathering/crystallinity sequence for the 1:1 layer silicates. The kaolin minerals appear to weather via halloysite and disordered kaolin to a well-ordered kaolinite characterized by large flakes and a high crystallinity index. Further weathering results in a reversal of the sequence via small flakes of highly disordered kaolin to gibbsite and ultimately perhaps to amorphous materials. The changes in the value of the crystallinity index as weathering proceeds are shown, together with changes downprofile and downslope.
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