A mysterious heavy metal found in the depths of the earth, slade is found, rarely, in massive structures, filled with dangerous creatures.
What little is known about slade is that it is impossible to mine it out with any tool currently known to dwarvenkind. Like adamantine, it radiates magic, but is less useful because of it's resistance to conventional mining. The discovery of slade is seen as a bad omen, as the creatures that dwell within the structures it forms are dangerous to even a mountainhome.
Slade has only ever been found forming massive underground structures, comparable in size to a palace. This has lead to some speculation that there was once a civilization capable of working the stone. The structures contain ancient zombies, many of races now rarely seen in the world.