Divers from Naples, Italy have retrieved a large block of chiseled obsidian believed to have been part of a Neolithic-era shipwreck near the island of Capri. The natural-glass block, approximately the size of a very large book and weighing nearly 17.6 pounds (8 kilograms), shows clear signs of chiseling on its surface. Archaeologists suggest it served as an obsidian “core,” used for producing sharp-edged flakes used in cutting tools.

The artifact was discovered by members of the Naples Police underwater unit at a depth ranging between 100 and 130 feet (30 and 40 meters) on Monday (Nov. 20), according to a statement from Italy’s Ministry of Culture. The find offers insights into ancient maritime trade routes and the use of obsidian during the Stone Age, highlighting its importance as a material for toolmaking and commerce in the Mediterranean region over 5,000 years ago.