The Pyrovile pod was an escape pod used by the Pyroviles. It was made of rock.
The surviving Pyroviles from Pyrovillia fled to Earth when their planet mysteriously disappeared. It crashed into the surface of Earth so violently, the Pyroviles were ground into dust inside the pod, which later became a control centre for Vesuvius, where they began to reconstitute themselves.
The Tenth Doctor and Donna Noble entered the pod and triggered the eruption of Vesuvius. The pod was tough enough to withstand the power of the volcano, and the Doctor and Donna survived the eruption. (TV: The Fires of Pompeii)