Zeiton-7

Zeiton-7 was a rare fuel which was used by TARDISes. It was used to generate orbital energy, which allowed the ship to move. It could be also used for fuel by other space-time vessels. It was generally found on Varos, though Galatron Mining Corporation had also found traces of Zeiton-7 on an asteroid. (TV: Vengeance on Varos)

The Eighth Doctor once suggested that it could be synthesised, perhaps using compressed nitrogen as a base but the exact formula eluded him. Zeiton-7 did not exist in the Divergent Universe. (AUDIO: The Creed of the Kromon)

Zeiton-7 could also be used to form part of a cold fusion generator. (PROSE: Lucifer Rising)

The Tenth Doctor fired up the Zeiton crystals as one of the steps to keep his TARDIS and his fifth incarnation's TARDIS from blowing a hole in the space-time continuum. (TV: Time Crash)