When coal is ground for use in a gasifier, the resulting particles will vary in physical and chemical make-up, in particular, the mineral amount and composition. The resulting ash composition distribution. by particle size and density, of ground Pittsburgh Seam coal was determined. The thermodynamically stable phases were calculated for each particle classification for a range of temperatures, with attention paid to the form of the non-slag phases, which must dissolve in the slag layer on the gasifier wall. Undissolved particles can be carried with the gas, resulting in fouling of downstream components. Results are separated into a comparison of the liquid versus solid phases formed, and a comparison of the phases formed for each particle type. Certain particle compositions form stable crystalline oxide phases that are usually incorporated into the slag at higher temperatures, while others can form metallic iron, which is stable even at high temperatures. (C) 2009 Elsevier B.V. All rights reserved.