Zeiton

Zeiton-7 was a rare minral and 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)

Zeiton-7 crystals were used to power tachyon-drive units. (COMIC: Buying Time)