Quantitative mineralogical analysis using a Rietveld-based X-ray diffraction method has been carried out on a succession of Permian coal seams and associated strata in a small but structurally complex area of the Gloucester Basin, New South Wales, to identify criteria that will assist stratigraphic correlation. The coals are relatively rich in mineral matter, which is dominated by quartz, illite and interstratified illite/smectite of detrital and pyroclastic origin. However, the mineral matter in the coals typically contains higher proportions of kaolinite and lesser proportions of illite than the associated noncoal strata, suggesting at least some leaching and reprecipitation of aluminosilicates in the original peat swamp. When considered on a quantitative basis, several of the seams contain distinctive assemblages in their mineral matter that can assist recognition of the seams in subsurface studies. These include an increased abundance of pyrite and feldspar in the marine-influenced upper Glenview seam, an increased abundance of well-ordered kaolinite in the upper Bowens Road seam, and a higher proportion of quartz in the lower Avon seam. The Roseville seam also contains measurable proportions of phosphate minerals, which are not detected in the other coal beds. Used in conjunction with other factors, quantitative mineralogical studies using XRD thus appear to be sufficiently sensitive to allow discrimination between individual seams in a sequence, even though the coals contain an abundant overprint of detrital and pyroclastic mineral components.