Coral

Coral can be found in the Oceans at the ends of the world. It grows on Sand Blocks within 250 tiles of the edges of the map and above the depth of 0 feet. The sand must be under at least 5 tiles of water. Background walls block its growth.

It can be harvested either with a hammer, by mining out the sand underneath it, or by placing a block next to it. It can be placed as a decoration and will have one of many appearances, much like Books. It is sometimes more than one block wide, so bear that in mind when placing other things next to it.