Mineralogy, chemistry and micromorphology of soils of a small watershed inthe costal plains of Espirito Santo State, Brazil

Soils of the coastal plains of the Espirito Santo state, Brazil, were studi ed with the objective of investigating and interrelationing their mineralog ical, chemical and micromorphological characteristics and to furnish subsid es for the pedogenetic environment reconstruction. Eleven soil profiles wer e described, collected and analysed. Less crystalline Fe by acid ammonium o xalate and amorphous Si by NaOH 0.5 mol L-1 were also determined. On mottle s and nodules samples the proportion of hematite and goethite and Al substi tution in goethite were analysed. Mineralogical analyses were performed thr ough optical methods, X-ray diffraction and differential thermal analysis. From undisturbed samples of subsuperficial horizons thin sections were prep ared for micromorphological analysis. It was found that the present pedogen etic environment is favoring kaolinite stabilization and goethite formation , removing hematite and being probably responsible for the yellowing (xanth ization) of superficial horizons. The process of iron segregation is eviden ced by its accumulation in nodules and mottles in relation to soil matrix, probably by diffusion, the source being the matrix. The red nodules and mot tles are in process of destruction instead of formation. The iron droplets which frequently occur in the interior of nodules and concretions constitut e a stage of the process of develop ment of these structures.