Lucidian (crystal)

Lucidian was a green crystalline substance, used by the species of the same name to fuel their spacecraft. Lucidian reflected and magnified emotion, making it so tangible that it could create physical effects. While being used, Lucidian would glow brightly, with warm colours such as white and orange accompanying pleasant emotions, and darker colours such as green accompanying unpleasant ones.

In 1852, the Tenth Doctor discovered seams of Lucidian crystal in the brickwork of an orphanage on Earth. This crystal had been amplifying the fear of the orphans, causing children to disappear, objects to come to life, and the building itself to take on a grotesque shape. The Doctor theorised that this material had found its way into the bricks after a Lucidian ship crashed into what would later become a quarry. (PROSE: The Shape on the Chair)