Nautical!

Nautilus shells, which are otherwise limited in use, become the base material for three tools and several building blocks. The Echoing Shell is crafted from one Echo Shard, one Nautilus Shell and a three-use durability item, and it lets a player echolocate nearby ores. Netherite works with it too. The Crystalline Shell uses an Amethyst Shard in place of the Echo Shard and lasts one use, and it reveals nearby ores and mobs for the player.

The mod also adds a Nautilus Shell Block, which is crafted from four shells and works as storage or decoration, along with Nautilus Shell Tiles and their stairs and slabs, made from two Prismarine Shards and two shells. A Nautilus Shell Horn plays sounds like a copper horn, with the pitch set by the direction the player faces. The mod runs on Fabric in client and server environments, so the server and every player need it. Its only published files are for 1.21.8 and 1.21.9, with 1.0.0 for 1.21.9 as the latest, and it is released under All rights reserved, so it is not open source.