Dissambiguation: This page is for the Marvel metal called Promethium. Not to be confused with DC's Promethium nor with real life Promethium (element 61).
Marvel's Promethium can always be found where the Soulsword is, as a heavy coat of armor can be summoned when a person swings the Soulsword around. However more skilled users, such as Dr. Doom, were able to instantly cover themselves in the powerful metal. Due to it's magical origins it does not rust, melt and its quite tangible. It also contained a power of it's own that was once sought out by Dr. Doom, as an inexhaustible energy source for Latveria.
When Darkoth was killed and then resurrected his entire body was composed of promethium, making him a fountain of magical energy. A person wearing this armor is also immune to the transmode virus. While promethium can be found as wild ore, its only within Limbo, in a hidden cavern in the form of an animal heart. If removed from the Limbo it causes the entire dimension to vanish.
Charnel was able to replicate the promethium by fusing nuclear reactors with raw magic, seeing as Death Metal was invincible, it assumed this promethium combination went well.