The behavior of quartz, kaolinite and calcite, as main components of coal mineral matter, has a direct impact on slags formations and development in pulverized coal combustion. The mineral transformations along temperature can be followed by differential scanning calorimetry (DSC). provided that the formation and crystallization of mullite (3Al(2)O(3). 2SiO(2)) are exothermic phenomena. Peak heights and areas allow to quantify the occurrence and extent of those mineral transformations for purr kaolinite and its mixture with calcite as fluxing agent. On the other hand, sinterization time at temperatures bellow mullite formation has a clear impact on the onset and the shape of the peaks. in this way, it is demonstrated that mineral transformations at solid state have a direct effect on the final structure of mineral species generated by slagging.