An in-depth characterisation was made of three U.K. bituminous coals and the combustion products from these coals when burned at a power station and on a range of experimental combustion facilities. CCSEM analysis of pulverised coals was performed to provide quantitative data on the size and chemical composition of individual mineral occurrences, and to determine the nature of the mineral-mineral and mineral-organic associations in the pulverised fuel. In a similar way, the size and chemical composition of individual fly ash particles has been determined. The coals were chosen to represent the range of ash compositions and slagging propensities found at U.K, power stations. The mineral-mineral association information was used to predict the effects of mineral coalescence; the dominant mineral transformation process for U.K. power station coals. The CCSEM information correctly identifies the types of mineral-mineral associations that are present, but underestimates the degree of association and hence the predicted effects of coalescence. The limitations of the information are inherent in the analysis of a polished cross-section, but useful information for the modelling of ash generation may still be obtained.