sedimentary
Coquina
Coquina (Bioclastic Limestone)
Hardness: 3 (Mohs), Color: Cream, white, or light tan, Luster: Dull to earthy, Structure: Fragmental/Bioclastic, composed of poorly cemented shell fragments, Cleavage: None.
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Physical properties
Hardness: 3 (Mohs), Color: Cream, white, or light tan, Luster: Dull to earthy, Structure: Fragmental/Bioclastic, composed of poorly cemented shell fragments, Cleavage: None.
Formation & geological history
Formed in high-energy marine environments (beaches) where waves accumulate shell fragments and coral debris, which are then lightly cemented by calcium carbonate (calcite). Generally recent to Pleistocene in age.
Uses & applications
Used as a construction material (historically for forts due to shock absorption), road base material, and in landscaping.
Geological facts
The Castillo de San Marcos in Florida is famously built from coquina; its porous nature allowed it to absorb cannonball impacts rather than shattering.
Field identification & locations
Identified by its 'oatmeal' appearance consisting almost entirely of crushed shells. Found primarily along coastal regions and barrier islands.
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