The clay mineralogy of soils from the moist southern Guinea savanna and subhumid northern Guinea savanna has been studied. All the soils occur on basement complex. Kaolinite is the dominant clay mineral in all the well‐drained soils, a property shared with the well‐drained soils of the humid tropical forests. In poorly drained soils montmorillonite forms in significant amounts in addition to kaolinite. Quartz is another mineral that occurs in the clay fraction of all the soils. Kaolinization is the dominant clay forming process under good soil drainage. The kaolinization process seems to be directed or favored by (i) the lowering of the pH of the weathering environment due to the temperature‐induced dissociation of soil water, (ii) marked leaching rainfall, and (iii) mineralogical composition of the soil or parent material. Under poor drainage montmorillonization becomes a significant clay‐forming process in addition to kaolinization due to the adequate silica, alumina, and base potentials of the soil solution.

Soils on four ironstone plateau near kalalawa, Adarawa, Bissalam and Tureta in Sokoto State were studied with the aim of a ascertaining their genesis, weathering status and soil mineral content. Morphological studies, total elemental analysis and X-ray diffraction were conducted for this purpose. The soils were found to have formed on weathered geological materials overlain by indurated ironstone crust. The geological weathered materials are Gwandu/kalambaina, Gwandu, Dange/Wurno and Gundumi formation on kalambaina, Adarawa, Bissalam and Tureta ironstone plateau respectively. The soils have good structural development and pronounced textural differentiation. The soils are well developed in terms of pedogenic processes (humification, mineralization, lessivation, homogenization and leaching) that have operated and are still operating to form the soils. Result of the silt/clay ratio, sesquioxide ratio and total Potassium, revealed a low weathering potential of the soils making them moderately weathered soils. The dominant mineral identified in the soils is quartz with kaolinite, feldspar and chlorite in trace amounts.

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The weathering of biotite in soils formed in saprolites derived from granite and gneiss was studied. The soils occurred in the Southwestern Upland of Nigeria which is characterized by a humid tropical climate.Vermiculite and montmorillonite are the usual products of biotite weathering in well‐drained temperature soils, whereas kaolinite appears to be the dominant product in the well‐drained, moderately acidic, tropical soils studied. The formation of kaolinitic pseudomorphs represented a stage in the kaolinization of biotite in the soils. A mechanism for the kaolinization of biotite has been suggested.