Mössbauer study of the Fe mineralogy in two different Argentine soils

Two Argentine soils featuring different characteristics and compositions (mollisols and ultisols) have been studied by Mossbauer spectroscopy and X-ray diffraction. The first type has a weakly developed profile with a solum thickness of 40 cm; the Fe oxyhydroxides are present in low concentrations in mixtures with other slightly weathered minerals (e.g., quartz, feldspars, 2 : 1 phyllosilicates, etc.). The second one is a typic kandihumult, which is a highly weathered red coloured, deep soil. The Fe oxyhydroxides are abundant, mixed mainly with kaolinite clay minerals. Analyses of iron mineralogy 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 both situations, but in the mollisol their content is much lower than in the ultisol. The mineralogy found is related to the different lithological characteristics and processes of pedological evolution on both soils.