Kaolinites with varying degrees of defect structures have been studied by both mid-infrared (IR) and near-IR diffuse reflectance spectroscopy (DRIFT). Difference bands were observed in the 2650-to 2750-cm (super -1) region. This region coincides with the kaolinite-deuterated hydroxyl stretching region. Summation bands were observed in the near-IR spectra in the 4500- to 4650-cm (super -1) and in the 7050- to 7250-cm (super -1) region. Each of the spectral regions of the summation and difference bands is both kaolin polytype and sample dependent. It is proposed that each of these sets of bands arises from the combination of the hydroxyl stretching frequencies and the hydroxyl deformation frequencies and, to a lesser extent, the silicon-oxygen symmetric stretching vibration of the siloxane layer. Additional difference bands of very low intensity were also observed at 2930 and 2856 cm (super -1) . Combination bands were observed in all kaolinites at 2137 and 2227 cm (super -1) . Each of the 3 major combination spectral regions was composed of 5 component bands corresponding to the 4 IR active and the 1 Raman active kaolinite hydroxyl stretching frequencies. Combination bands were also observed at approximately 1932 and 1821 cm (super -1) .

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