The chemical composition of slag transfer is usually expressed in terms of simple oxides calculated from elemental analysis determined by x-ray fluorescence. Table 18-2 lists the range of compounds present in steel slag from a typical base oxygen furnace. Virtually all steel slags fall within these chemical ranges but not all steel slags are suitable as aggregates. Of more importance is the mineralogical form of the slag, which is highly dependent on the rate of slag cooling in the steel-making process.