The U. S. Geological Survey has been interested for some time in how rocks became contaminated by trace elements during grinding before analysis. Elimination of contamination is especially important in emission and x-ray spectrochemical analysis.
A. T. Myers and W. H. Wood, "Ceramic Mills in a Paint Mixer for Preparation of Multiple Rock Samples," Appl. Spectrosc. 14, 136-138 (1960)