The chemistry of spinels, plagioclase, and iron-rich, normally zoned pyroxene and melilite from some metallurgical slags has been investigated by electron microprobe analysis. Minor element partition coefficients, some of which are composition-dependent, have been calculated from the analytical data. The pyroxene/liquid partition coefficients range from 4.03 to 0.03 in the order Ti/Zr, Al, Mn, Zn, Ba, Sn, Na, reflecting increasing incompatibility. The spinel/liquid partition coefficients range from 40.89 to 0.02 but in the order Ti, Ni, Mg/Zn, Al, Mn, Cu, Sn, Zr. However, Sn becomes very compatible when the pyroxene and spinels crystallize in association with cassiterite. Melilite greatly discriminates against the incorporation of minor elements into its crystal structure. The crystallization of these phases produces residual liquids enriched in Na, Mn, Zn, Sn, Ba, W, and Pb.