Coquina is a type of limestone that is composed primarily of the broken shells and fragments of marine organisms, such as mollusks and corals. It is a sedimentary rock that is formed when these shell fragments and other debris are deposited and cemented together over time. Coquina is typically found in coastal environments, where it can form beaches, dunes, and other geological features. Due to its composition, coquina is a relatively soft and porous rock that is often used as a building material or for decorative purposes.