Clay mineralogy of soils from SW Spain with high iron content

Abstract

The mineralogy of the clay fraction of four soil one alfisol and three inceptisols developed on cambian limestone, and to consider the mode of formation in terms of pedogenic processand classification has been determined. In soils I and II there is a high proportion of goethite accompanied by hematite at the bottom of the profiles, according to the data goethite is originated directly from the bedrock and hematite is produced by dehydration of goethite. The most characteristic is the presence of maghemite in the upper horizon of these profiles. Its presence is related with the weathering of hematite, that may produce goethite and later maghemite by dehydration. The non-ferrous minerals of soil are: talc, chlorite and interstratified talc-chlorite, profile II has in addition to kaolinite, vermiculite and illite. In soil IV a high proportion of goethite and hematite has been found, a high relation exist between bath iron oxides. The hematite is originated directly from the bedrock and goethite is produced from hematite. The high proportion of kaolin is characteristic, showing an external contribution or extensive pedogenic processes. Soil III is constituted by goethite and hematite and it is difficult to determine, the origen of these iron oxides. The non-ferrous minerals are kaolinite, chlorite and illite.