Pietra del Vesuvio, from Mt. Vesuvius, Naples, Campania, Italy
Geological description:
A porphyritic lava/dyke rock, probably a trachyandesite, showing a large cognate inclusion with a reaction rim. It has euhedral phenocrysts of pyroxene, feldspar and olivine. The fine-grained groundmass contains the same minerals set in devitrified glass or zeolite.