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Abstract

In lateritic profiles from Cameroon, the relationships between ferruginous nodules, in which the texture has been inherited from the parent rock, and surrounding red and yellow matrices, in which the original rock texture has disappeared, were investigated by optical and scanning electron microscopy and by electron microprobe, X-ray powder diffraction, infrared, and electron spin resonance analyses. An orderly succession of changes was found for kaolinite from the ferruginous nodules to the clayey matrices as follows: (1) successive generations of the clay, each of smaller particle size; (2) concomitant decrease in degree of crystallinity; (3) increase in amount of iron substitution; and (4) decrease in the degree of orientation relative to the foliate texture of the parent gneiss. Correlative changes were also observed for associated iron oxides: (1) progressive decrease in the overall content of iron oxides; (2) decrease in the content of hematite (containing a minor amount of Al substitution); and (3) an increase in the content of Al-substituted goethite. These data suggest successive transformations from the ferruginous nodules to the surrounding clayey matrices, although progressive recrystallization may have taken place due to variation of the geochemical conditions of weathering of the original rock.

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