Hargstone

Hargstones were valuable jewels found in the arctic region of Centuria. They had many industrial uses. Among these, they could be used to maintain temporal stasis machines.

When a group of Cybermen were created by thief from stolen Torchwood Archive files, they captured the human inhabitants of Centuria and converted half into Cyber-drones to mine hargstones. (COMIC: Drones of Doom, Enemy Mine)