CHARACTERIZATION OF HYDROXY-INTERLAYERED VERMICULITE AND ILLITE-SMECTITE INTERSTRATIFIED MINERALS FROM THE WEATHERING OF CHLORITE IN A CRYORTHOD

X-ray diffraction, FTIR, and chemical analyses were performed on clay fractions (1-2 mum, < 0.1 mum), separated by means of size fractionati ons and high-gradient magnetic separation techniques, from a Cryorthod developed in a chlorite-mica schist saprolite. Weathering of large ph yllosilicates pre-existing in the saprolite involves physical fragment ation and mineralogical transformations. Chloritic minerals in the coa rse fractions were the most affected by physical breakdown, while mica s were generally preserved. As a consequence, a concentration of mica layers occurred in the coarse clay fraction, while chloritic residues accumulated in the fine clays. These residues exhibited the typical XR D pattern of hydroxy-interlayered intergrade minerals, but the interla yered contaminants were found to be mainly hydroxy-Mg cations. Further mineralogical transformations of the intergrade minerals involved the progressive removal of the hydroxide interlayered sheet and dissoluti on of chloritic layers. Illite/smectite mixed-layers were formed in th e surface horizon of the soil profile. These processes were associated with a strong decrease in Fe and Mg contents in the clay fractions.