Coral Block

Coral block is a solid block which comes in five variants: tube, brain, bubble, fire, and horn.

Dead coral block is a solid block which comes in the same variants as coral blocks.

Obtaining
Coral blocks can only be obtained with a pickaxe enchanted with Silk Touch, otherwise they will drop the respective dead coral block. Dead coral blocks can be obtained with any pickaxe.

Natural generation
Coral blocks and dead coral blocks naturally generate in coral reef structures. These are found in warm oceans.

Usage
Coral blocks and their dead variants can be used as building or decoration blocks.

Dead coral blocks
In order for coral blocks to stay alive, at least 1 of the blocks surrounding it must be water. If placed outside of water, it will transform into its respective dead coral block after a while.

Despite presumably being alive, splash potions of harming will not damage them, and the Wither will not prioritise their destruction over other blocks.

Trivia

 * On the Bedrock Edition, horn coral blocks and brain coral blocks have a different texture than on Java.
 * Meanwhile, the dead variant of this block is the same.
 * After players had placed 10 million coral blocks underwater, Mojang donated $100,000 to The Nature Conservancy to protect and restore coral reefs around the world.