Mixtures of coal and refuse-derived fuel (RDF) were burned and the fly ash was collected and analyzed for concentration trends with respect to RDF/coal ratio and particle size. RDF contributes more Ca, Mn, Sb, and Pb to the fly ash while coal contributes greater amounts of As, Br, Hf, Ni, Sc, V, and the rare earths. Smaller particles in the RDF fly ash had higher concentrations of As, Cd, Ga, K, Na, Sb, and the rare earths. RDF fly ash contains four distinct morphologies, exhibits a high specific surface area, and does not resemble fly ash derived from a conventional coal-fired power plant. The morphology of the ash helps explain the high solubility of many species in the RDF-rich fractions.