sedimentary
Coquina
Bioclastic Limestone
Hardness: 3 (Mohs scale), Color: tan, gray, or cream-colored, Luster: dull to earthy, Structure: poorly cemented fragments of shells and coral, Cleavage: none (irregular fracture), Specific Gravity: 2.3-2.5
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Physical properties
Hardness: 3 (Mohs scale), Color: tan, gray, or cream-colored, Luster: dull to earthy, Structure: poorly cemented fragments of shells and coral, Cleavage: none (irregular fracture), Specific Gravity: 2.3-2.5
Formation & geological history
Formed in high-energy marine environments like beaches and barrier islands where wave action accumulates sand-sized shell fragments. Most surficial deposits date from the Pleistocene or Holocene epochs.
Uses & applications
Used primarily in construction for building stone or roadbed material. In the past, it was used for fortification walls due to its ability to absorb cannon fire rather than shatter.
Geological facts
The Castillo de San Marcos in Florida is the most famous structure built from coquina; it proved indestructible against British naval cannons in 1702 because the soft rock compressed rather than splintering.
Field identification & locations
Easily identified by its 'breakfast cereal' appearance of visible, broken shell fragments. Commonly found along the Atlantic coast of Florida and the Carolinas.
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