Mineralogical characterization of iron-rich clayey soils from the middle plateau in the southern region of Brazil

We report mineralogical studies of clayey soils collected in various sites of the middle plateau in Rio Grande do Sul in the southern region of Brazil. The analysis of the XRD patterns indicated quartz, rutile, goethite, hematite and kaolinite in the samples. Mِssbauer spectroscopy has been used to study the Fe-bearing species. The Mِssbauer spectra of all the samples at room temperature consist of a large paramagnetic doublet, in some cases superimposed on a small sextet, whereas at 77 K a prominent sextet appears, which is associated with goethite and/or a hematite substituted structure. The results indicate that the studied soils have iron oxides with high contents of aluminum.