coquina

noun

1. Also called pompano, butterfly-shell clam. a small clam, Donax variabilis, abundant in the intertidal zone of eastern and southern U.S. coastal beaches, having fanlike bands of various hues, the paired empty shells often spread in a butterfly shape.
2. any similar clam, especially of the genus Donax.
3. a soft, whitish rock made up of fragments of marine shells and coral, used as a building material.

noun

1. a soft limestone consisting of shells, corals, etc, that occurs in parts of the US

1. A soft porous limestone, composed of shells and fragments of shell and coral that are partially cemented by material that is high in calcium carbonate and has not completely hardened.