Polygrite

Polygrite was a material that could be found many places in the universe. The Terileptils used it in their control bracelets. On Earth in the year 1666, the Fifth Doctor noticed that the necklace Richard Mace was wearing, actually a broken control bracelet, was made of polygrite, proving that the comet that fell recently was actually a spacecraft. (TV: The Visitation)
Category:Inorganic substances