Malampus crystal
From Tardis Wiki, the free Doctor Who reference
Malampus crystal could be mined from the Crystal Mountains of Malampus. The Malampans used the crystal to see auras and divine inner truth.
Stonn purchased a Malampus crystal whilst visiting Cardiff and gave it to Tom Foster as a gift. They used it as a lens for Tom's camera, allowing them to capitalise on the spiritualist craze. The negatives created the Revenants, which was discovered by Madame Vastra who convinced Stonn to smash the lens. (AUDIO: A Photograph to Remember)
