The fly ash from the Jungar Power Plant, Inner Mongolia, China, is unique because it is highly enriched in alumina (Al₂O₃>50%). The fly ash mainly consists of amorphous glass and mullite and trace amounts of corundum, quartz, char, calcite, K-feldspar, clay minerals, and Fe-bearing minerals. The mullite content in fly ash is as high as 37.4% because of high boehmite and kaolinite contents in feed coal. Corundum is a characteristic mineral formed during the combustion of boehmite-rich coal.Samples from the economizer were sieved into six size fractions (<120, 120-160, 160-300, 300-360, 360-500, and >500 mesh) and separated into magnetic, mullite+corundum+quartz (MCQ) and glass phases for mineralogical and chemical analysis. The corundum content increases but amorphous glass decreases with decreasing particle size. Fractions of small particle sizes are relatively high in mullite, probably because mullite was formed from fine clay mineral particles under high-temperature combustion condition. Similarly, fine corundum crystals formed in the boiler from boehmite in feed coal. The magnetic phase consists of hematite, magnetite, magnesioferrite, and MgFeAlO₄ crystals. The MCQ phase is composed of 89% mullite, 6.1% corundum, 4.5% quartz, and 0.5% K-feldspar.Overall, the fly ash from the power plant is significantly enriched in Al₂O₃ with an average of 51.9%, but poor in SiO₂, Fe₂O₃, CaO, MgO, Na₂O, P₂O₅, and As. Arsenic, TiO₂, Th, Al₂O₃, Bi, La, Ga, Ni, and V are high in mullite, and the magnetic matter is enriched in Fe₂O₃, CaO, MnO, TiO₂, Cs, Co, As, Cd, Ba, Ni, Sb, MgO, Zn, and V. The remaining elements are high in the glass fraction. The concentration of K₂O, Na₂O, P₂O₅, Nb, Cr, Ta, U, W, Rb, and Ni do not clearly vary with particle size, while SiO₂ and Hg decrease and the remaining elements clearly increase with decreasing particle size. ?? 2009 Elsevier B.V.