A Harmonised mithril rock is a special rock that can appear in the Trahaearn Clan district's mining area in Prifddinas while the Voice of Seren is active for the clan. The rocks can give an endless supply of ore until they collapse after a fixed amount of time, however more can appear. The mining experience is the same as the regular rocks; however, because they can only appear with the Voice of Seren active, there will always be an experience boost active when they appear.