The transformations of mineral matter during pulverized coal combustion were followed by CCSEM (Computer Controlled Scanning Electron Microscopy) analysis for several char samples collected in the course of combustion. It was found that the included minerals in coal mainly coalesced to form larger fly ash particles, while fragmentation took place for the liberated minerals. A new method to predict the distribution of fly ash size and chemical composition at a given combustion degree was developed using the CCSEM analysis of the feed coal. Calculated results gave good agreement with measurement data.