sampietrino

noun

1. A roughly 12cm square-topped, dark, fine-grained, paving stone with a tapered base, endemic to Rome (first used in the 17th century to pave St. Peter’s Square—whence it received its name—later becoming iconic throughout Rome and further afield in Italy), which was traditionally (albeit not exclusively) quarried from the mafic, alkaline, ultrapotassic leucitite Pleistocene-age lavas erupted by the Alban Hills volcano just outside of the city, although modern replacement stones are often made of similar, yet more readily-available, cheaper basalt, imported from China.
2. One of the highly-skilled, hereditary craftsmen exclusively entrusted with the upkeep of St. Peter's Basilica since 1600 CE, as well as the lighting and decoration of its exterior during the annual Feast of Saints Peter and Paul.