X-ray diffraction and infrared characterization of Oxisols from central and southeastern Brazil

Eleven Oxisols with high clay contents, 2.6-59.7 wt.% Fe 2 O 3 , and containing hematite, goethite, magnetite and maghemite, from Sao Paulo, Minas Gerais and Goias, Brazil, were studied for the purpose of microwave remote sensing applications in the 0.3 to 300 GHz range. Of special interest are: the pseudosand effect caused by Fe-oxide cementation of clusters of soil particles; the mineralogy; and whether the soil magnetic susceptibility affected by ferromagnetic magnetite and maghemite interferes with microwave propagation. Quantitative mineralogical analyses were conducted using X-ray diffraction with Rietveld refinement. Visible, near infrared and short wave infrared spectroscopic analyses were used to characterize the samples qualitatively for comparison with published spectral radiometry results. Quartz (3-88%), hematite (2-36%) and gibbsite (1-40%) occurred in all soils, whereas kaolinite (2-70%) and anatase (2-13%) occurred in nine samples. Ilmenite (1-8%) was found in eight soils and goethite (2-39%) in seven. Of the ferromagnetic minerals, maghemite occurred in seven soils (1-13%) and three contained magnetite (<2%). These results will be applied to the interpretation of the effect of Fe oxides, particularly the ferromagnetic oxides, on microwave interaction with high-Fe soils, with ultimate application to the monitoring of soil water content by microwave remote sensing.