The Hardened Sand Block is a type of block, along with Sandstone Blocks, that make up the Underground Desertbiome. It looks similar to Sand Blocks, with an altered texture and slightly different color. Unlike sand, it is not affected by gravity. Like all sand-based blocks, it has Corruption, Crimson, and Hallowed counterparts: Hardened Ebonsand, Hardened Crimsand, and Hardened Pearlsand respectively.
In Hardmode, Hardened Sand Block is a "corruptible" block, and can be converted to its corrupted version of Hardened Ebonsand, Hardened Crimsand, and Hardened Pearlsand, and spread the corrupted biome to nearby corruptible blocks.
A player equipped with Dunerider Boots will be able to run faster while standing on any type of Hardened Sand Block.