Silver

Silver was a metal with an atomic weight of 108 and high conductivity. (PROSE: Castrovalva)

In human mythology, silver could be used to kill a werewolf, particularly in the form of bullets. The First Doctor used silver bullets to kill Roberta Sampson, a werewolf. (PROSE: The Juror's Story)

Silver bullets were also utilised by the Brigadier to defeat the Destroyer. (TV: Battlefield)

Similarly, Rosa Caiman had a silver knife to defend herself against werewolves. (AUDIO: Loups-Garoux)

The planet Megerra was rich in valuable minerals such as silver. (PROSE: Shakedown)

Daleks with silver casings and blue domes were present on the temporary base the city of Andor on Moldox. (PROSE: Engines of War)

When forced to create EDTA to cure arsenic poisoning, Gwen Cooper used a number of ingredients in the antidote, one being silver. (TV: Rendition)