Obsidian Totems are usually found in deserts. Breaking the totem yields 3-4 Obsidian Totem blocks and an Obsidian Tile block.
Obsidian Totems are used with a Crystal Core in the construction of Mystical Constructs that can move aura nodes.
There are cases where one can find the totems on hills and in a circular pattern with obsidian tile used as sporadic flooring. The totem circle yields 3-4 obsidian per totem and some upon the flooring. In the center of the circle is a chest that yields Dungeon loot. Under the obsidian tile it sits upon lies a wisp spawner.
The wisp spawner spawns standard wisps that have no additional Aspect.
An Unstable Node sits in the center, with a Vis around 420 - 610. The Flux is moderate.
Approach with caution.
Additionally, Pigmen can also spawn in such circle patterns; the loot may also include items such as Sword of the Zephyr or Shovel of the Earthmover (not just Thaumium tools).
Totem circle with node in center