Coal combustion in stoker boilers is characterized by the low rate and long time of combustion and the biggest size of coal feed grains. Several types of cooccurrence of chars and transformed inorganic matter were distinguished. Minute (< 1 mum) inorganic particles are disseminated within chars. Bigger (over 2 mum) particles are stuck to char walls and pores and also sometimes occur within pores. In some cases. they are also stuck into char walls in such big quantities that carbonaceous matter is almost invisible and acts as a binding material. Thin (< 1 - 3 mum) inorganic matter layer coat external char walls or walls of internal pores, Inorganic matter can also be intermixed with chars and next resolidified. The individual types of cooccurrence are dependent on coal plasticity and mineral matter behaviour during combustion. (C) 2002 Elsevier Science B.V. All rights reserved.