In Moroccan calcareous mountains, red soils are distinguishable from brown 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. This can 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 pseudoparticles from red soils and an increase of amorphous Fe has 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 of hematite by dehydration of ferrihydrite.