The Collaborative International Dictionary of English v.0.48:

Coquina \Co*qui"na\, n. [Sp., shellfish, cockle.]
   A soft, whitish, coral-like stone, formed of broken shells
   and corals, found in the southern United States, and used for
   roadbeds and for building material, as in the fort at St.
   Augustine, Florida.
   [1913 Webster]