Halkonite puzzle box

Halkonite puzzle boxes were made from Halkonite steel. They were impenetrable. Nothing could escape them, not even thoughts.

In 2008, Sarah Jane Smith used a box made of Halkonite steel to contain a fragment of the Weserbergland meteorite where the Pied Piper had been trapped. (TV: The Day of the Clown)

Behind the scenes
According to the official SJA website the box is from a place called Halkon.