SPECTRAL (MIR) DETERMINATION OF KAOLINITE AND GIBBSITE CONTENTS IN LATERITIC SOILS

Kaolinite and gibbsite are the fundamental components of lateritic soi ls, along with iron oxides and oxyhydroxides and residual quartz. The relative proportion of these two minerals are a probe of the degree of development of these soils, which explains the importance of quantita tive measurement. The relative proportion is usually determined using chemical analysis or X-ray diffraction, which are time consuming and c ostly techniques. A new procedure, based on diffuse reflectance spectr oscopy, is proposed to estimate kaolinite and gibbsite abundances in l ateritic soils. for kaolinite, the analysis concerned only the content in the clay fraction of the fine residue. In addition, an index was f ound, that could estimate accurately the ratio K-i = SiO2/Al2O3 in lat eritic soils. These measurements may be conducted directly in the fiel d using a portable spectrometer.