Photoacoustic FT-IR spectroscopy was used to quantify kaolinite in binary mixtures with KBr and silica, with the use of a linear relationship between the reciprocals of photoacoustic intensity and kaolinite concentration. The method is valid for both dilute and concentrated mixtures; an average error of 12% was obtained for kaolinite concentrations ranging from 15 to 80%. The technique thus compares favorably with more common approaches that require low analyte concentrations. It is concluded that quantitative photoacoustic infrared spectroscopy is feasible provided that the magnitude of the product of thermal diffusion length and absorption coefficient is taken into account.