Gold

Gold is a chemical element much prized by Humans, and a major weakness of Mondasian Cybermen.

The Animus could control beings that were in contact with gold, which lead to it controlling the Zarbi.(DW: The Web Planet)

The Lady Peinforte would dip her gold-headed arrows in poison as her "calling card".(DW: Silver Nemesis)

Prospecters flocked to Mal Oreille mistakenly beliving its yellow-algae infested seas to be rich in gold deposits (BFBS: Missing Adventures: Biology Lesson on Mal Oreille).

Owing to its non-corrossive nature, gold essentially choked the Cybermen's respiratory systems. The glittergun, a weapon used during the Cyber-Wars, fired gold dust at its targets to exploit this weakness.(DW: Earthshock) Gold appeared to affect some varieties of Cybermen in the way that silver affected werewolves, so that gold coins or gold-tipped arrows fired at them had the same effect. (DW: Silver Nemesis) It is unknown if gold affects the Cybus Cybermen of Pete's World.

During a time period in which the Cybermen had been reduced to small remnant groups wandering around the galaxy, one group tried to take revenge by making a desperate attempt to blow up the remnants of the planet Voga, a planetoid of pure gold that had wandered into the Sol system and become a moon of Jupiter. They hoped that this would disrupt their enemy's supply of the element. (DW: Revenge of the Cybermen)