Abstract: A method and apparatus for determining the size distribution of certain particles, of a particular composition, such as iron sulfide (pyrites), in a sample of host material, such as coal. Data representative of the amount of at least one predetermined elemental constituent of the particles is obtained for each of numerous similarly-sized subsamples of the sample. The "constituent amount" data for each subsample is sorted into bins, each representative of a respective constituent amount range in a series of constituent amount ranges. Respective scaler representations of the fraction of the constituent amounts, represented by each bin range, are provided to yield an approximate representation of the distribution function of the amounts of the constituent in the subsamples of the coal. Those scaler representations collectively may provide a histogram.