Timothy P. Rose, Robert E. Criss,
Department of Geology, University of California, Davis, CA 95616, USA
George R. Rossman
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
Visible discrimination of quartz and feldspars can be greatly facilitated by the irradiative coloration of mineral concentrates using gamma-radiation from a 137Cs source. Irradiated quartz samples typically become smoky colored. Sanidine phenocrysts generally acquire a yellow color while plagioclase and plutonic K-feldspars respond weakly or negligibly to irradiation. Manual separation of 0.25 - 3.0 mm mineral grains that were initially identical in appearance was readily accomplished following radiation treatment. Available data indicate that this process does not modify the chemical or isotopic composition of the sample.