As mollusks develop in the sea, their mantle tissue absorbs salt and chemicals. They secrete calcium carbonate, which hardens on the outside of their bodies, creating a hard shell. ... The mollusk continues to take in salt and chemicals from the sea and secrete calcium carbonate, which makes its shell grow even bigger.

How a seashell is formed?

“A seashell is a protective outer coating secreted by the animal's mantle, which is one of their muscles,” she said. The mantle forms the soft outer wall of their body. ... A mollusk produces calcium carbonate from its mantle, laying down layers of it over its lifetime. Together, those layers form the seashell.

How are shells naturally made?

Seashells are the exoskeletons of mollusks such as snails, clams, oysters and many others. ... Mantle tissue that is located under and in contact with the shell secretes proteins and mineral extracellularly to form the shell. Think of laying down steel (protein) and pouring concrete (mineral) over it.