Giant's Heart
From Tardis Wiki, the free Doctor Who reference
The Giant's Heart was a living creature that resembled a black diamond and absorbed light.
It was discovered on Earth by Count Otto Von Harnstein and presented to Queen Victoria in 1897. It was guarded by Vastra, Jenny Flint, and Strax in the Tower of London until it could be cut and set into Queen Victoria's crown. The Doctor arrived to take the creature to the Dying Sun of Dhrush where it could absorb light for ages. (PROSE: The Giant's Heart)
