A technique is described whereby measurement of the mass absorption coefficients of minerals can be used to give an estimation of the mineral composition. Direct measurements of on chemically analyzed plagioclases demonstrates the applicability of the method. The straight line regression so derived from 41 plagioclase samples gives the following equation: An % = 25.27 , with a standard deviation of 1.61 % An.
The method can be extended to other solid solution series, such as olivine, orthopyroxene and zincblende series, and calculated values of for different members of these series are presented. By judicious selection of the wavelengths of the absorbed X-ray beam the effects of interfering elements can be reduced to a minimum.
Although the experimental work reported in this paper was done using an X-ray spectrograph, measurements of μ can be made using a diffractometer.
The advantage of this method over other indirect methods for determining mineral compositions is that the measured values of μ are directly related to the chemical compositions of the samples.