Coquina
- For the variety of clam, see Donax .
Coquina (Spanish, "cockle"; Template:PronEng) 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 County to Palm Beach County. It may occur up to 20 miles inland from the coast in the sub-surface. 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
Occasionally quarried or mined and used as a building stone in Florida for over 400 years, coquina forms the walls of the Castillo de San Marcos, Saint Augustine. 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
- Washington Oaks State Gardens, Flagler County, Florida
- House of Refuge, Hutchinson Island, Martin County, Florida
- Blowing Rocks Preserve (and along Country Club Road), Palm Beach County, Florida
- North Carolina Aquarium at Fort Fisher, features a "Coquina Outcrop Touch Pool"
See also
External links
