sedimentary
Coquina / Fossiliferous Limestone
Biogenic Calcite (CaCO3)
AI-generated identification · may be incorrectMohs hardness 3; cream to tan color; dull, earthy luster; composed of cemented shell fragments; highly porous.
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Physical properties
Mohs hardness 3; cream to tan color; dull, earthy luster; composed of cemented shell fragments; highly porous.
Formation & geological history
Formed in shallow marine, high-energy beach or barrier environments where broken molluscan shells accumulate and cement over time.
Uses & applications
Used historically as a building stone (notably in fortifications like the Castillo de San Marcos) and locally for aggregate.
Geological facts
Because of its porous, unconsolidated nature, coquina can absorb cannonball fire without shattering, making it famous in historic Spanish colonial forts.
Field identification & locations
Identified by its obvious, poorly cemented accumulation of crushed seashells and rapid reaction (fizzing) with dilute hydrochloric acid.
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