Basalts are large rocks which can't be moved or destroyed. They occur frequently in later worlds of Adventure Mode or sometimes as part of a Set Piece in Sandbox Mode and can come in the form of a pillar.
Apart from decoration or forming an indestructible blockade (similar to the Tree Clump) it serves no other purpose.
- Players can use the Imprisoned Pig Set Piece in which Basalt spawns to trap any kind of mob, even giants in Reign of Giants, and hold them prisoner there without fearing their escape. An easy way to trap them is craft a Telelocator Focus inside the "prison" and then use the Telelocator Staff on the desired mob. But using the staff near the trap is not advised, because the sanity drain would lower the obelisks, thus allowing the creature to escape.