Hardened Sand Block

The point of hardened sand is that gravity ignores it. Loose sand collapses the moment you mine underneath, which makes desert tunneling miserable and makes sand close to useless as a building material. Hardened sand reads as the same thing at a glance but behaves like stone, so it is what you reach for when you want the desert look on a ceiling, an overhang, or anything above head height.

Like the rest of the desert layer it converts once the world turns. Corruption, Crimson, and Hallow each have their own version of the block, and each version pushes its biome into whatever convertible blocks sit next to it. Cleaning up an infected desert means dealing with the hardened sand underneath, not only the surface you can see.

Dunerider Boots count it as desert ground and speed you up over it, which adds up on long paths. A Portable Kiln turns it straight into pots wherever you are standing, handy for dressing up a desert build without hauling clay around. The infected versions melt into glass exactly like the clean block, so there is no need to purify a stack before you use it.