Belstar

 was a planet that the Sixth Doctor and Peri Brown once visited. Geologically rich with gold, it was, at the time of their visit, a world plagued by war between its two technologically advanced species, the Siros and the Debans. Other planets in its star system were Lostar and Kristar. In the war, a key strategic area of the planet was the Nomed Zone, wherein could be found the blue rock, a crystal containing what the Deban leader called "all the secrets of [Lostar and Kristar]". (PROSE: Battle Planet)