The Baltimore mafic complex in the central Appalachian Piedmont consists of tectonically emplaced layered ultramafic, mafic cumulate, and volcanic rocks. The general stratigraphy of the layered rocks is basal dunite and chromitite grading upward through lherzolite and websterite to hypersthene gabbro and quartz-gabbro at the top. Cyclicity within the cumulus sequence is shown by the presence of upper-level peridotite and the occurrence of olivine gabbro at higher stratigraphic levels. The cumulus crystallization sequence is olivine plus chrome spinel followed by orthopyroxene, clinopyroxene, and plagioclase. Cryptic variation in the composition of the cumulus minerals is shown by olivine Mg_97–75,...