Swenyo was a rare ore found on few planets. It had the rare property of giving off psychic energy which could be used in battle computers.

One of the few places it could be found was Callous, where the Master, in preparation for Last Great Time War, manipulated people and events to get a large deposit of it, as part of a mission for the Time Lords.

When trying to mine the ore, races like the Ood were vulnerable to it and got driven insane by it. (AUDIO: Sins of the Father)

Even Time Lords were affected by it, finding it uncomfortable. (AUDIO: The Persistence of Dreams)

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