Red Lyrium
You don't know what your power has done to me, I want to know if I'll heal inside. Another hole in the wall of my inner defenses, leaving me breathless, the reason I know that I am stricken and can't let you go.
Red lyrium is a corrupted and corrupting version of normal lyrium that is somehow inherently evil despite supposedly being an inanimate mineral. The strange substance was first found by Hawke and Varric Tethras during a trip to the Deep Roads. Varric’s brother Bartrand found an idol made of red lyrium, took it, and trapped everyone else in the chamber, leaving them to die. When he reappeared years later, he was completely insane. The idol, and a piece of it that Bartrand had broken off, were eventually recovered and disposed of. Since that was all of the material that had made it out of the Deep Roads, that was thought to be the end of it. However, after the explosion at the Temple of Sacred Ashes during the Conclave, red lyrium began to appear on the surface in Ferelden and Orlais. It turned out Corypheus and his minions were spreading the substance for their own nefarious ends.
The Inquisition did a lot of research on red lyrium to try and find ways to counter it. The stuff started off bad and the more we learned, the worse it got. While underground, red lyrium appears in the same vein-like shapes that regular lyrium does, but aboveground it forms into crystals that range from tiny to building-sized, and that spread on their own. It gives off heat and seems to weaken the Veil around it, allowing spirits and demons to cross over from the Fade more easily. When ingested, it actually corrupts a person from within, slowly transforming them into more of the substance. We observed this in the alternate-future version of Redcliffe Castle, and in the actual timeline with the Red Templars, who were tricked into consuming the stuff by Corypheus. It is said that red lyrium “sings” to those who are exposed to it, like its normal counterpart, but the red variety also causes people to hear voices and go mad. And if that sounds familiar, there’s a disturbing reason for that. During our adventure with dwarf Bianca, she told us that the mind and body-warping substance was regular lyrium infected by the taint. We later learned, during our trip below the Deep Roads of the Storm Coast, that lyrium was actually the blood of some kind of ancient rock-beings called titans. So, lyrium was part of a living organism, meaning it could absorb the taint and become red lyrium. That is why red lyrium affects people in many of the same ways as the darkspawn taint, because it effectively is the darkspawn taint. Removing the stuff once it takes hold is virtually impossible as well, whether we’re talking about a piece of land or a person. Only the truly depraved would use it as a weapon, and its use and spread is just another item on the lengthy list of reasons why Corypheus had to be stopped.