The ash transformation and deposition behavior of pyrite and illite, which are commonly identified with slagging, are influenced by the manner in which the minerals occur in the fuel. An enhanced computer controlled scanning electron microscopy technique was used to analyze the mineral content of individual coal particles in samples of two pulverized fuels. The particle-by-particle analysis determined whether individual mineral grains were included or excluded. It also provided information on which mineral species were likely to be found in the same coal particle with pyrite or illite. Illite typically appeared as included particles and was associated with a variety of other silicate species. In contrast, pyrite tended not to associate with other minerals and showed a significantly higher fraction of excluded particles. Such detailed observations of coal mineral distributions and associations provide additional insight into the mechanisms which govern fly ash formation.