An X-ray diffraction method has been successfully applied to the quantitative determination of mineral mixtures. The absorptive properties of the samples and the number of components determine the analytical procedure to be used. The methods described (external standard plus empirical determination of the mass attenuation coefficient) provides an accurate and rapid alternative to the direct measurement of the mass attenuation, Compton diffusion or internal standard methods. The relative accuracy obtained is of the order of 10% at the 0.1% level, independent of the sample composition.