sedimentary

Coquina

Biogenic calcarenite / Coquina (CaCO3)

Hardness: 3 (Mohs scale); Color: Cream, tan, or grey; Luster: Dull/Earthy; Structure: Clastic fossiliferous; Cleavage: None; Porosity: High.

Hardness: 3 (Mohs scale)
Color: Cream, tan, or grey
Luster: Dull/Earthy

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 3 (Mohs scale); Color: Cream, tan, or grey; Luster: Dull/Earthy; Structure: Clastic fossiliferous; Cleavage: None; Porosity: High.

Formation & geological history

Formed in high-energy marine environments where shell fragments accumulate and are cemented together by calcium carbonate. Most deposits are relatively young (Pleistocene to Holocene).

Uses & applications

Used as building stone, especially in historical coastal fortifications like the Castillo de San Marcos, and as road base material.

Geological facts

The word 'coquina' is Spanish for 'small shells'. It is famous for being 'soft' enough to absorb cannonball impacts rather than shattering, making it a superior material for historic forts.

Field identification & locations

Commonly found along coastal areas in Florida, North Carolina, and Australia. Identified by the visible, often loosely cemented fragments of shells and coral.