Amnesium
From superman.nu: Supermanica
Amnesium
A rare space metal. The rays of this material makes the affected forget recent memories.
Jimmy Olsen holds a jar of this material while looking at Superboy's mineral collection when he was sent by mistake to the past. Superboy then sends him back to the future holding the jar, making him forget the whole trip. (SA No. 1, 1960: "A Visit from Superman's Pal")
