Route: Located at 68.0S 62.2W on the south side of the Obsidian Plains. The Dangerous Portal mansion statue drops you nearby (1 of 3). The Tusker mansion statue can also drop you reasonably close (1 of 3).
Lore & Dialog
Obsidian Node Golem tells you, "The Master keeps me here to keep the node pure. I am the watcher against the blight of T'thuun. I guard the node of the Obsidian Plain. I require Blighted Mana Crystals to maintain function. If you supply such crystals to me or my fellows at the other nodes of Dereth, you will be recognized and rewarded."