Room temperature Mössbauer spectra of bulk Chilean soil samples derived from volcanic materials (Ultisols and Andisols) are very complex and least-squares fitting not seldom leads to many different interpretations. In most cases the presence of commonly occurring iron oxides in those soils, namely maghemite (ideal formula, g Fe2O3), hematite ( gFe2O3) and goethite (aFeOOH) in Andisols, and maghemite, magnetite (Fe3O4), ferrihydrate (Fe5HO8.4H2O) and/or goethite in the Ultisol can only be speculated. In the present paper we present X-ray diffraction and Mössbauer analyses of particle size fractions (soil, sand, silt and clay), which were submitted to magnetic extraction (sand fractions) and subsequently to NaOH selective chemical treatment (silt and clay fractions), in laboratory procedures which were conveniently adapted to such volcanic soil-samples. When chemically treated soil separates of Ultisol are analyzed, the presence of partially oxidized magnetite is confirmed, and the existence of hematite is also inferred. The magnetic fraction separation and chemical treatments are to be essential steps in sample preparation in the mineralogical assessment of Chilean soils derived from volcanic materials