The mineralogical composition of the clay fraction (2$) of two soil profiles from Izaña and Portillo, have been studied by X.ray diffraction and I. R. absorption techniques, Minerals of the kaolin group, mainly halloysite, are predominant in the clay speciments, and disordered knolimite is present. Illite is also found in some soils horizonts. Primary minerals presaent in the clay fraction of bath profiles are felspars. Piroxenes. quartz, a-crystoballite and hemaities qre also found in some soils horizonts.

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