Lithium

Lithium was an element.

According to the Eighth Doctor, Lokic fields were simply hydrogen, helium, and lithium. (AUDIO: The Witch from the Well)

Lithium citrate patches counteracted the influence of Keratin gold pulses on the human brain for several hours. (AUDIO: The Glittering Storm)

The Kaldor Company Fusion Plant used lithium and sea water to synthesise deuterium and tritium. (AUDIO: The Sentient)