Vitanium

Vitanium was an exceedingly rare mineral. According to the Sixth Doctor, vitanium was used as a power source in most hyperspeed space drives, including the drive systems of Dalek saucers. It was extremely valuable.

Because it was found in abundance on Omnia, the Daleks invaded in order to mine the planet for this mineral. Many native Omnians were sent to vitanium mines as punishment for defiance, and never seen or heard from again. (AUDIO: Emissary of the Daleks)