sedimentary
Coquina or Fossilized Shell Aggregate
Calcareous bioclastic sedimentary rock (CaCO3)
Hardness: 3 (Mohs scale), Color: Cream, tan, or grayish-white, Luster: Dull to earthy, Crystal Structure: Amorphous/Microcrystalline, Cleavage: None (variable fractures), Specific Gravity: 2.3-2.5
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Physical properties
Hardness: 3 (Mohs scale), Color: Cream, tan, or grayish-white, Luster: Dull to earthy, Crystal Structure: Amorphous/Microcrystalline, Cleavage: None (variable fractures), Specific Gravity: 2.3-2.5
Formation & geological history
Formed in high-energy marine shoreline environments where shell fragments accumulate rapidly. Most specimens date from the Holocene to Pleistocene epochs.
Uses & applications
Used as a construction material, for road base, decorative landscaping, and occasionally as a source for lime.
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
Identify by its 'oatmeal' or 'macaroni' appearance where individual shell segments or worm tubes are visible. Found primarily along coastlines in Florida, North Carolina, and Australia.
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