It's all over Vvardenfell; why there we all know to be caused by Lorkhan's Heart being cast down there.
But what about the locations in Skyrim?
The ebony ore veins at the very tip-top of the Throat of The World may have some linking to the fact that it's the peak of a Tower...
...But what about Gloombound Mine, next to the orc stronghold of Narzulbur in the Eastmarch Hold? Why is there so much in there?
EDIT: And Shor's Stone too? what relevance does the mine's 'red mist' there have?