Hargstone
From Tardis Wiki, the free Doctor Who reference
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)
