Coral

Corals are crafting materials which can be found in the Ocean biomes at the ends of the world. They grow naturally on Sand Blocks underwater and within 250 tiles of the edges of the map and above the depth of −10 feet /  0 feet, as long as no more than 5 Corals are within a 7-tile range. Corals can be harvested either with a pickaxe/drill, by mining out the sand underneath them, or by placing a block above them. Corals can be placed for decoration and will have one of many appearances, much like Seashells.

Corals will spawn slower on sand under less than 5 tiles of water. Spawn rates scale with rain, wind and empty space up to 14 tiles above the Sand Block.

Corals will only spawn on sand under at least 5 tiles of water. Rain and wind do not affect spawn rates.

Trivia

 * s are animals.
 * On earlier versions, while each piece of Coral only needed one block under it, it essentially took up an extra half-space on each side, preventing walls or objects from being placed directly to either side. For example, to place 5 Corals between walls, one would have needed the walls to be at least 11 tiles apart. To fit the same 5 Corals on an open platform, it only needed to be 9 blocks wide.