Shells come from animals called mollusks, which include snails, clams, oysters, and others. These soft-bodied animals have an outer layer of tissue called the mantle that creates their shells. Specialized cells in the mantle secrete proteins and minerals, primarily calcium carbonate, which forms the hard protective outer covering of the shell. This shell grows as the animal grows, forming layers and sometimes colorful patterns depending on the species and its diet. When the mollusk dies, its empty shell can be found washed up on beaches or in the ocean.
The shell is not part of the animal's living body itself, but a hard casing made from minerals the mollusk secretes for protection from predators and the environment. The shell has three layers: an outer protein-rich layer, a middle layer with calcite crystals for toughness, and a smooth inner layer called nacre or mother-of-pearl made of aragonite crystals. Over time, empty shells can break down and become part of the sand on beaches.
