Tiantianium

Tiantianium was the most precious metal in the galaxy, as it could propel a starship for over a year. In 2266, Spock detected traces of tiantianium ore on the planet Metamorpha, prompting the USS Enterprise (NCC-1701) to investigate. After returning the planet's chemistry to its original state, which also restored the native Metamorphans to their physical forms, the Enterprise crew were allowed to extract two hundred pounds of tiantianium ore.