Gallium

Gallium was an element on the periodic table.

Mars was abundant with gallium, deuterium, palladium, and silver. (PROSE: Beige Planet Mars)

The Seventh Doctor believed creating trees that could grow on asteroids was simple enough if one used gallium arsenic solar cell leaves driving the pico-electric systolic pumping system and an atavistic silicon outer shell. (PROSE: The Also People)