Pietra dell'Etna, from Mt. Etna, Catania, Sicily, Italy
Geological description:
An altered crystal-rich ignimbrite. Amygdaloidal microporphyritic rock clasts with altered subhedral phenocrysts of a ferromagnesian mineral and feldspar, are set in very fine-grained dark matrix. Amygdales are rounded or irregular in shape, and many contain carbonate infills which have a banded agate-like appearance. The streaky appearance of paler patches suggests a flattened shard structure.