Prismarine

Prismarine is a stone-like material that only appears underwater in ocean monuments. This block has several variants, including prismarine bricks and dark prismarine.

Obtaining
Prismarine can be mined using any pickaxe. If mined without a pickaxe, it will drop nothing.

Natural generation
Prismarine naturally spawns in ocean monuments. Deconstructing the monument yields a lot of prismarine, but is non-renewable and takes a long time.

Crafting
Prismarine can be crafted with 4 prismarine shards in the inventory crafting grid or crafting table. This method requires a large quantity of shards, but is renewable, and the demand can be easily met with a guardian farm.

Trivia

 * The name "prismarine" was created by Reddit user AjaxGb during a naming contest, where Jeb was looking for a name for the block.
 * Its name is composed of prism, referencing how a glass prism creates rainbows out of white light, and marine, since it is an underwater block.
 * Prismarine appears similar in color and texture to the real-world microcline.
 * The cracks in prismarine slowly change color between brown, blue, gray and purple.
 * The full animation for the prismarine texture takes 5 minutes and 30 seconds to complete.