Coke obtained from Syncrude and Suncor was investigated to characterize the metals and minerals by ashing it at various temperatures. Samples were collected by high temperature ashing at 100 degrees C intervals from 400 to 1200 degrees C. Samples were also obtained from low temperature ashing (LTA) which gives little effect on the mineral assemblage compared to HTA samples. X-ray diffraction patterns of Suncor and Syncrude coke ash were analyzed qualitatively and quantitatively to characterize the mineral phases in the sample and their thermal transition behavior. In Suncor ash, kaolinite, illite, gypsum, anhydrite, microcline, anorthite, hematite, sillimanite and quartz were dominant phases in ash from the LTA temperature up to 700 degrees C, and mullite, cristobalite, hercynite, albite, anorthite, pseudobrookite and other iron-titanium oxides were dominant mineral phases from 700 to 1200 degrees C. In Syncrude ash, illite, anhydrite, quartz, anorthite, microcline, sillimanite and hematite were dominant up to 700 degrees C, and hercynite, anorthite, albite, pseudobrookite and other iron-titanium oxides were dominant up to 1200 degrees C. The higher quantities of Ca, K and Na, and the lower quantities of V, Fe and Ni in Syncrude ash resulted in higher amorphocity and the different mineral phases. (C) 2006 Elsevier Ltd. All rights reserved.