One of Cornwall’s best-known geologists visited the excavation and gave his expert comment on the stones. Colin Bristow told us that the monument lay right on the contact zone of the Carmenellis granite and the lower-lying killas.
He suggested that the stones were probably sourced from the area and that they had not been moved at any great distance by the Neolithic community who erected this impressive portal dolmen.
One distinctive feature of the capstone is the presence of xenoliths, small spotted blotches (no more than 10cm in diameter), which pepper the surface of the granite capstone. These xenoliths are fragments of killas and their presence indicates that the capstone was originally not far from the granite edge.