Buried treasure is a naturally-generated structure added to Minecraft as part of 1.13 - The Update Aquatic.
Buried treasure consists of a hidden Chest, buried several blocks underground. It can spawn in almost any Biome, including Ocean Biomes. The chest can contain a wide variety of loot, including enchanted Armor and Tools. It usually contains Diamonds, Emeralds, Gold Ingots and Prismarine Crystals. There will always be a Heart of the Sea inside.
- Buried treasure is the only way to obtain a heart of the sea outside of the creative mode inventory or Commands.