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FIGURE 1. Powder XRD scans showing the mineral phases in expanded vermiculites. (a) Two scans of differing count times of Zonolite; the 2–17° scan (with count time of 8 s) shows the three mineral phases routinely found in an expanded vermiculite product with each of the peaks labeled and keyed to hydrobiotite (hy), vermiculite (ve), and biotite (bi), and an 8.5–11.5° scan with a 180 s count over the location of the 110 amphibole peak as well as the 003 hydrobiotite peak. (b) Two stacked XRD scans of the unspiked Black Gold sample with range and count times as in Figure 1a. Notice the three mineral phases in the lower scans and that K-exchanging the sample "collapses" them into the single biotite peak, thus removing the interference of the 003 hydrobiotite peak with the 110 amphibole peak. (c) This scan is a K-exchanged sample from Libby clearly showing presence of the 110 amphibole peak.
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scan is a count time of 8 s and the shorter 180 s. (a) A subset of the spiked samples showing the 1000 ppm sample’s 110 peak that is our detection limit, and the relationship between the 110 peak area and added amphibole. (b) The top most scan is the bg_10000 ppm spiked sample with the unknown attic samples plotted in decreasing order of % amphibole. (c) A series of scans with differing count times for the bg_10000 ppm spiked sample, showing that at the 1% level, amphibole is detected by XRD at count times much less than the 180 s we used for our calibration method.