NATURE DES OXYDES DE FER DANS LES SOLS DU BRÉSIL RÉPARTITION EN FONCTION DU CLIMAT

Iron oxides occurring in Brazilian soils and its relationships with climate ABSTRACT - Goethite and haematite are the main iron constituants of the Brazilian lateritic soils. Haematite and especiall) goethite present distinct degrees of Al substitution according to the distribution of the soils in the different bioclimatic regions. The goethite which has a higher degree of AI substitution are found in the Red Latosols of Central Brazil which presentsa marked seasonal climate. Goethite is associated to agreat amount of haematite and gibbsite. Both of these disappear either in the humid zone of Amazon and Subtropical regions or in the arid zone of the Northeastern region. In Amazon and Subtropical regions, in well drained soils, the goethite presents a rather high degree of Al substitution. In the Northeastern region, the rate of Al substitution varies according to the different topographic levels : in the old pedological covers associated to the higher levels the goethite presents a higher AI substitution rate while in the younger pedological covers of the lower levels the goethite has a low degree of Al substitution and can be associated to a small amount of haematite. Ferrallitic soils, Haematite, Goethite, Gibbsite m