Troth Glenbeard was a dwarf with a mission. And that was destruction.
From there, things happened. And the Irondeeps got a Subterranean-Transport-System-That-Moves-Things-Around-Faster-Than-Equine-Means (aka, in modern-speak, a subway).
Mining in a certain area turns all exposed skin (maybe just parts that are actively disturbing the chemicals that cause the reaction) of the those doing the mining to a dark blue color. Will wear off taking as many years/days spent in the mine.