Mossbauer study of the Fe mineralogy in two different Argentine soils

Two Argentine soils featuring different characteristics and compositions (m ollisols and ultisols) have been studied by Mossbauer spectroscopy and X-ra y diffraction. The first type has a weakly developed profile with a solum t hickness of 40 cm; the Fe oxyhydroxides are present in low concentrations i n mixtures with other slightly weathered minerals (e.g., quartz, feldspars, 2:1 phyllosilicates, etc.). The second one is a typic kandihumult, which i s a highly weathered red coloured, deep soil. The Fe oxyhydroxides are abun dant, mixed mainly with kaolinite clay minerals. Analyses of iron mineralog y show hematite and goethite in both soils. Their ratio is low in the first case and high in the last case. Magnetite-maghemite are also present in bo th situations, but in the mollisol their content is much lower than in the ultisol. The mineralogy found is related to the different lithological char acteristics and processes of pedological evolution on both soils.