Pietra dell'Etna, from Mt. Etna, Catania, Sicily, Italy
Geological description:
Altered (?phonolitic) tephrite. A porphyritic rock with prominent euhedral megacrysts of black pyroxene, and with an altered euhedral pale mineral forming less obvious phenocrysts. The groundmass is very fine-grained, fawn-coloured, and of indeterminate mineralogy. This sample has some similarities with no. 665 but is lighter in colour, possibly because of alteration.