The Corrupt Obelisk is a decorative object the size of two blocks in height that "spreads" Corruption and gives off a dim light.
This object can be crafted in your Crafting Menu (default key "Q") or at Crafting Tables (that can still be found on older worlds), but only after the crafting-recipe has been unlocked by
- crafting (or taking) Corrupted Stone Walls for the first time (unlocked after mining Corrupted Stone with at least a Diamond Mining Cell)
- obtaining Lumite (Bars) made in a Forge from Lumite Ore that can be found in Nodes on the Corruption layer deep underground
- crafting Lumite Walls from Lumite Bars, Diamond Rods and Globs of Goo
- and obtaining Crystal Shards from creatures like Pigsies either as a loot or pet-harvest, or alternatively made from Tourmaline in a Processor
To craft 1 Corrupt Obelisk you'll need (as of August 2016):
- 4 (blocks of) Corrupted Stone mined from the Corruption layer, which requires at least a Diamond Mining Cell
- 4 Crystal Shards, obtained from Creatures like Pigsies or made from Tourmaline in a Processor
- 1x Corruption Dust, either looted or Pet-harvested from any corrupted creature: Corrupted Pigsy, Corrupted Leafi, Corrupted Chizzard, Corrupted Miru or the Thing
- 1 Lumite (bar) made in a Forge from Lumite Ore found on the Corruption layer underground, extracted with any kind of Extractors
- Diamond Rods made from Diamond (bars) in a Forge from Diamond Ore found on the Lava layer underground
Mind that Corrupt Obelisks can corrupt blocks of green Grass and any kind of Wood if you place the Obelisks on or directly next to them, even without needing to wire them up to any activation device first.
While Corrupt Obelisks will only corrupt 4 neighbouring blocks and the one directly below (not diagonally, not two blocks in height), Corruption can then spread further to other Wood blocks touching the corrupted one/s.
Corrupt Obelisks can be named (like storage chests) by interacting with them ("f" as the default key or right-click) after being placed.
Additionally to that with a Wiring Tool Corrupt Obelisks can be wired with Switches, Pressure Plates, Sensors or Number Pads, optionally together with gates such as Number Comparison Gates, Logic Gates, Flip-Flop Gates, Inverter Gates or Delay Gates. The dim light of Corrupt Obelisks can switched on/off by using the activation devices then.
Currently corruptable blocks under and next to Corrupt Obelisks will be corrupted by them even if the Corrupt Obelisk is "turned off".