A rapid, very low cost of instrumentation and simple approach to specimen preparation for the analysis by X-ray fluorescence spectrometry is presented. This technique requires a few mg of powdered samples, which are compressed to produce pellets. This procedure is employed for determining major, minor and trace elements in muscovites and K-feldspars. Factors affecting measured intensities, such as particle size and distribution, surface texture, pelletizing pressure, etc, are considered. A description of the new sample preparation device, including technical characteristics, is also given. It is demonstrated that suitable specimen presentation to the X-ray beam is obtained by using our procedure.Fil: D`angelo, José Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Química de San Luis. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Química de San Luis; ArgentinaFil: Strasser, Edgardo. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia; ArgentinaFil: Marchevsky, Eduardo Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Química de San Luis. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Química de San Luis; ArgentinaFil: Perino, Ernesto. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia; Argentin