Belstar

 was a planet that the Sixth Doctor and Peri Brown once visited. Other planets in its star system were Lostar and Kristar.

Belstar was geologically rich with gold, and at the time of the Doctor and Peri's visit was plagued by war between its two technologically advanced species, the Siros and the Debans. 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)