Comparative clay mineralogy of the “terra roxa estruturada” soil in the amazon region

Abstract

The mineral composition in the clay fraction of the “terra roxa estruturada” (TRE) soils from Altamira county in the Brazilian Amazon region was discussed by comparing with that of a neighboring red yellow podzolic soil using X-ray diffraction method, differential thermal analysis and chemical analysis. Kaolinite was dominant in the TRE soils. Hematite and goethite were detected, but gibbsite was not found in these soils. The TRE soils were characterized by relatively high content of hematite which acts as a cementing material, judging from a very rare existence of the microaggregate in the red yellow podzolic soil contained an extremely small amount of hematite. The stable micro-aggregate of the clay particles cemented by hematite results in good physical condition of the TRE soils, and make the soil fertile, although their chemical properties are not always good.