The thermal and compositional conditions of magma chambers constrain the type and complexity of their metasomatic aureoles. Fragments of these aureoles, disrupted during explosive eruptions of Vesuvius, provide quenched snapshots of interactions between potassic magmas and carbonate country rocks. Near the highly crystallized peripheral portions of the chambers, represented by magmatic xenoliths (fergusites, syenites and pyroxenites), skarn aureoles form. Open conduit reservoirs and the lower portions of plinian and subplinian eruption magma chambers develop aureoles controlled by diffusive metasomatism by high-T-modified silicate melts, generating magmatic skarn. In contrast, infiltrative metasomatism by magmatic fluids exsolved from crystallizing margins is responsible for endoskarn (magmatic protolith) and exoskarn (carbonate protolith) formation in the upper portions of plinian and subplinian eruption magma chambers.