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For the variety of clam, see Donax .


Coquina outcropping on the beach at Washington Oaks State Gardens, Florida


Coquina (Spanish, "cockle"; ) is an incompletely consolidated sedimentary rock. Coquina was formed in association with marine reefs and is a variety of "coral rag", technically a subset of limestone.

Composition and distribution

Coquina is mainly composed of mineral calcite, often including some phosphate, in the form of seashells or coral. It is found in surface exposures along the east coast of Florida from St. Johns Countymarker to Palm Beach Countymarker. It may occur up to 20 miles inland from the coast in the sub-surface. It is found as far north as Fort Fisher, North Carolina. It has also been formed in the South Island of New Zealand, where it outcrops in a disused quarry near Oamaru. The Oligocene deposits here are composed primarily of very well preserved brachiopod shells, in a matrix of brachiopod, echinoid, and bryozoan detritus and foraminifera.

History and use

Coquina from Florida.
Close-up of coquina from Florida.
The scale bar is 10 mm.
Occasionally quarried or mined and used as a building stone in Floridamarker for over 400 years, coquina forms the walls of the Castillo de San Marcosmarker, Saint Augustinemarker. The stone makes a very good material for forts, particularly those built during the period of heavy cannon use. Because of coquina's softness, cannon balls would sink into, rather than shatter or puncture, the walls of the Castillo de San Marcos.

When first quarried, coquina is extremely soft. This softness makes it very easy to remove from the quarry and cut into shape. However, the stone is also at first much too soft to be used for building. In order to be used as a building material, the stone is left out to dry for approximately one to three years, which causes the stone to harden into a usable, but still comparatively soft, form.

Coquina has also been used as a source of paving material. It is usually poorly cemented and easily breaks into component shell or coral fragments, which can be substituted for gravel or crushed harder rocks. Large pieces of coquina of unusual shape are sometimes used as landscape decoration.

Because coquina often includes a component of phosphate, it is sometimes mined for use as fertilizer.

Notable exposures of coquina



See also



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