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Preparation procedures are examined by which the length of amosite fibres may be reduced so that preferred orientation is removed thereby providing samples suitable for quantitative X-ray diffraction analysis. Grinding in methyl alcohol produced samples from which X-ray diffraction gave major peak intensities reproducible to within ±2%. X-ray analysis has been carried out on samples of either calcium silicate powder or a lagging material which consists largely of a calcium silicate matrix reinforced with rockwool fibres which contain known additions (≤ 10 wt %) of amosite. The limits of detectability of amosite in both of these matrix materials, based on three diffraction peaks 110; 060:310; 240, have been established. It is concluded that for a mixture of amosite in calcium silicate powder, the limit of detectability is 0.4± 0.1 wt % and for amosite in lagging material, the limit of detectability is 0.2± 0.1 wt %. These are discussed in terms of differences in the physical distribution of the matrix materials.