sedimentary

Coquina / Shell Limestone

Coquina (Bioclastic Limestone)

AI-generated identification · may be incorrect

Hardness: 2-3 (Mohs scale), Color: Cream, tan, or white, Luster: Dull/Earthy, Crystal Structure: Amorphous/Bioclastic, Cleavage: None/Irregular, Specific Gravity: 2.3-2.5

Identified April 2, 2026More sedimentary →

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Physical properties

Hardness: 2-3 (Mohs scale), Color: Cream, tan, or white, Luster: Dull/Earthy, Crystal Structure: Amorphous/Bioclastic, Cleavage: None/Irregular, Specific Gravity: 2.3-2.5

Formation & geological history

Formed in high-energy marine environments (beaches/reefs) by the accumulation and mechanical sorting of shell fragments, coral, and other organic debris. Generally formed in the Cenozoic era to recent times.

Uses & applications

Used primarily in construction (historical buildings), as a decorative landscaping stone, and occasionally in road surface material in coastal areas.

Geological facts

Coquina is historically famous for its use in the Castillo de San Marcos in St. Augustine, Florida. The stone's porous nature allowed it to absorb cannonball impacts rather than shattering.

Field identification & locations

Identify by looking for visible shell fragments cemented together. It will react and fizz (effervesce) if a small drop of weak acid like vinegar or HCl is applied due to its calcium carbonate content.