sedimentary
Coquina
Coquina (Bioclastic Limestone)
Hardness: 2-3 (Mohs scale), Color: tan, cream, or light brown, Luster: earthy to pearly, Structure: clastic (fragmental), Cleavage: none, Specific Gravity: 2.2-2.4
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Physical properties
Hardness: 2-3 (Mohs scale), Color: tan, cream, or light brown, Luster: earthy to pearly, Structure: clastic (fragmental), Cleavage: none, Specific Gravity: 2.2-2.4
Formation & geological history
Formed in high-energy marine environments where waves break and accumulate shell fragments. They are typically of Holocene to Pleistocene age (within the last 2.5 million years) and occur in coastal zones.
Uses & applications
Historically used as a building stone (notably in Florida and the Caribbean) because it is soft enough to quarry but hardens with exposure. Also used for road base and landscaping.
Geological facts
A famous example of Coquina architecture is the Castillo de San Marcos in St. Augustine, Florida. It is effectively a 'natural concrete' made entirely of fossilized shell debris.
Field identification & locations
Identify by looking for a mass of poorly cemented, coarse shell fragments with visible voids between them. Common in coastal areas like Florida, the Outer Banks, and shark teeth-rich deposits.
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