A characterization study was performed on the spent oil shale (oil shale ash) obtained from the combustion of Jordanian oil shale. This characterization utilized different analytical techniques. These include scanning electron microscope with energy dispersive spectrum analysis, X-ray fluorescence. X-ray diffraction and Qemscan. During the combustion process, minimal fragmentation was encountered since Jordanian oil shale contains large proportions of ash which maintain the original structure of the oil shale particle. Different analytical techniques confirmed that the dominant phase of minerals in the oil shale is calcite, which transforms. in parts, into anhydrite during combustion. Sulphur was found to be mainly of an organic source. This sulphur is combusted to produce SO2 and then SO3, which controls the sulphation reaction of the calcite. The dominant phase in the ash was the anhydrite in addition to the calcite, clays and calcium phosphate. (C) 2004 Elsevier Ltd. All rights reserved.