sedimentary
Coquina / Shell Limestone
Coquina (Bioclastic Limestone)
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
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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.
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