A perfectly spherical object the size of a ping pong ball, found in Number Four's Loric Chest, its official name and function is unknown, although it is hinted that it is a form of tracking beacon, possibly connected to the Macrocosm, as Mogadorians found Four, Six and Sam shortly after it was touched.
In Four's chest the crystal was glowing and brightened when Number Six picked it up. It began to pulse with light and dimmed when she dropped it. Whilst holding it Six felt pin pricks against her palms and a "bad feeling". Four describes his stomach compressing and acid crawling up his throat.
It is currently wrapped up tightly in Four's chest.