Contribució al coneixement mineralògic d'uns sòls laterítics de l'Alt Volta

Abstract

The mineralogical composition of samples of a soil which has developed on top of granitic material in the Ouagadougou region (Upper Volta) is studied using the techniques of: X-ray diffraction, infrared spectrometry and differential thermal analysis.
The results obtained indicate the presence in the profile of kaolinite as the only neoformation of clay mineral, grains of quartz and small quantities of anatase and illite as inherited materials, iron oxides: hematite, goethite and amorphous gels such as hisingerite.
These minerals are found in the samples in a clayey-ferruginous material which contains quartz grains and pisolites in which the goethite is mainly concentrated. No outstanding changes are observed in the profile except for the disappearance of the pisolitique structures at a depth of 1'10 m, although different coloured mottles continue to be present.
On account of the above mineralogical composition, these soils could be included in the sub-class of ferralytic soils, ferralytics with kaolinite group (DUCHAUFOUR, 1977), in which this clay mineral dominates and weathering has almost totally destroyed the clays 2:1, thus not succeding in forming gibbsite. These soils do not correspond to the actual climate of the region studied, and so they could form part of the abundant relict soils of the region (BOULET, 1970), whose origin would date from the most humid and warm periods of African Pleistocene.