Letter. Quantification of amphibole content in expanded vermiculite products from Libby, Montana U.S.A. using powder X-ray diffraction

Abstract

Five expanded vermiculite samples known to have originated from the former vermiculite mine near Libby, Montana were analyzed using powder XRD to quantify their amphibole content. An expanded vermiculite with no detectable amphibole based on our XRD methods discussed herein was spiked with 100, 500, 1000, 2500, 5000, 7500, and 10 000 ppm Libby amphiboles to determine the detection limit of XRD and to develop a calibration method. The 110 amphibole peaks were not detectable in the 100 and 500 ppm samples; thus, defining the detection limit. The 110 peak areas for the remaining samples were measured and used to form a calibration curve relating peak area to ppm amphibole. Of the five Libby samples, each had detectable levels of amphibole and their amphibole content ranged from 1171 to 9218 ppm. The XRD method provides a bulk measurement of the total amphibole content. To determine the amount of asbestiform amphiboles, morphological considerations obtained by microscopy techniques are required. From the results of a previous polarized light microscopy study, the five expanded vermiculites in this study would contain from 390 to 3073 ppm asbestiform amphiboles and not be subject to regulation on the basis of the 1% rule used by regulatory agencies in the U.S.A.