Cuttlebone

Cuttlefish (Sepia sp.) in Komodo National Park

A piece of cuttlebone washed up on a beach.

Cuttlebone (also referred to as cuttlefish bone) is the internal shell of a cuttlefish (Family Sepiidae).

It is commonly used as a supplemental source of calcium since it is natural, brittle, and easily ingested.

Cuttlebone is primarily composed of aragonite, a crystalline form of calcium carbonate (CaCO₃).