Sandstone Block

A common mistake when clearing an underground desert is ripping out every sandstone block and expecting the spawns to stop. They will not. What decides whether the game counts a room as underground desert is the unsafe Sandstone Wall in the background, so the walls are the thing to remove. The blocks themselves have no say in it.

Corruption, Crimson, and Hallow each convert sandstone into their own version, and those versions do carry a biome and push it into neighboring convertible blocks. An underground desert is one of the faster places for an evil biome to run loose, since the layer is mostly connected sand. Infected sandstone is also a dead end for building, because only the clean block can be smoothed into Smooth Sandstone while the tainted ones give you walls and nothing else.

Antlion Eggs slowly grow back on clean sandstone anywhere below the surface, not just inside a desert, so a sandstone floor is a renewable supply. Dunerider Boots speed you up on any sandstone surface, which makes a sandstone road a cheap way to cross a large desert base. And the naming is a trap: Sandstone Brick has nothing to do with this block.