SPECTROSCOPIC APPROACH FOR INVESTIGATING THE STATUS AND MOBILITY OF TI IN KAOLINITIC MATERIALS

The form under which Ti occurs in kaolinitic materials from various en vironments has been investigated using second derivative diffuse refle ctance spectroscopy. The position of the absorption edge may be used a s a diagnostic band to determine:Ti-phases (anatase, rutile, Ti-gels). Ti-oxides may be detected in kaolins, down to 0.1 wt. % TiO2. Diffuse reflectance spectra show the presence of Ti-gel-like phases occluded in sedimentary kaolinite particles. These phases, which record conditi ons at the time of kaolinite growth, constitute the first direct evide nce of Ti mobility at the scale of mineral assemblages and question th e substitution of Ti for Al in kaolinite. The nature of the Ti-oxides associated with kaolinite particles gives some constraints on the temp erature conditions of hydrothermal kaolins, the evolution of sedimenta ry kaolin during basin diagenesis and the source of parental material in soil kaolins.