Ash-fusion characteristics of the Lower Kittanning seam (western Pennsylvania) can be related to environment of deposition. Non-slagging coals (coals with ashes that have ash-fusion temperatures [AFTs] in excess of 2,600°F) are associated with freshwater environments that occur toward the margins of the basin. Slagging coals (coals with ashes that melt at temperatures less than 2,200°F) occur in the central part of the basin, in areas overlain by shales that have been interpreted to have formed in a brackish environment. Trend-surface analysis indicates that whereas strong basinal trends do exist, locally variability can modify regional trends. High ash-fusion coals are associated with high clay (primarily kaolinite) contents, whereas low-fusion coals are associated with high pyrite and marcasite (and to a lesser extent, siderite) contents. Bivariate analysis of these data shows highly significant negative correlations between AFT and Fe 2 O 3 , pyrite, and siderite. Positive correlations exist between AFT and SiO 2 , Al 2 O 3 , TiO 2 , MgO, and K 2 O. Illite and kaolinite also correlate positively with AFT. An understanding of the oxide and mineral composition of the ash and the depositional environment of the peat can therefore be useful in the prediction of ash-fusion characteristics.