User blog comment:Dragongod00/Acnologia's true element/@comment-1776824-20150919080052

Dragons use magic in general, and their roars are just an extension of that ability. Like how not all magic is elemental in nature, not all dragons have an elemental affinity. Iron is not a typical element, for instance. However, as we've seen with Weisslogia and Skiadrum, dragons may also possess forms of magic other than what they use in their roars in such. Ergo, Zirconis may indeed have destructive roaring capabilities, like the others, but he only cast that one type of magic via his breath. But, we'll get more info on Acno in due time, anyway.