HEMATITE IDENTIF ICAT ION IN PSEUDO- PART ICLES OF MOROCCAN RUBIF IED SOILS

not only by their colour but also by their microaggregated structure. Clay mineral dispersion studies of these soils were carried out by increasing pH, after different treatments. The formation of the pseudo-particles appears to be dependent on the fixation of amorphous Fe on clay and on the chemical binding of those clays by amorphous Al-hydroxy-polycations. Thiscan be explained by the high isoelectric point of ferric compounds such as ferrihydrite which are soluble in ammonium oxalate. Based on these results and using techniques of granulometric analysis, red clays aggregated in pseudo-particles were separated from less rubified clays. Hematite was identified in pseudo-particles from red soils and an increase of amorphous Fehas been shown in aggregated clays. These microstructural conditions characterizing rubification could also favour it, by creating microsites where water activity decreases and allows the crystallization f hematite by dehydration of ferrihydrite. Soil rubification in Mediterranean and temperate climates has been widely studied resulting in contradictory hypotheses which have advanced greatly in recent years due to the use of modern techniques. Originally, authors were in agreement regarding the important role of dehydration o