Prismarine Shard item in Minecraft

What it does

Four shards in a square make a Prismarine block, nine make Prismarine Bricks, and eight around a black dye make Dark Prismarine. Each of them has slabs and stairs, and plain prismarine also has a wall. Prismarine slowly shifts colors, which makes it stand out in underwater and sea-themed builds.

Four shards with five prismarine crystals make a Sea Lantern, a bright light that works under water as well as on land.

Guardian farms built around ocean monuments are the usual way to collect shards in bulk, since breaking the monument itself requires a lot of mining.