Coral Caverns

The coral caverns is an underground biome where the blocks consist of various types of crushed coral and often have small pools of water scattered around its interior.

The coral blocks are affected by liquids to a minor degree and will turn into dark coral once dark water gets comes into contact with it.

There seems to be a higher possibility of the biome spawning on ocean and tidewater planets, with the entire cavern consisting of dark coral if found on a tidewater planet.