sedimentary
Coquina
Coquina (Bioclastic Limestone)
Hardness: 3 (Mohs scale), Color: Cream, tan, or gray, Luster: Dull to earthy, Structure: Fragmental/Clastic, Cleavage: None (distinctly porous)
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Physical properties
Hardness: 3 (Mohs scale), Color: Cream, tan, or gray, Luster: Dull to earthy, Structure: Fragmental/Clastic, Cleavage: None (distinctly porous)
Formation & geological history
Formed in high-energy marine environments where waves accumulate shell fragments and coral debris, which are eventually cemented by calcite. Most deposits are relatively young (Pleistocene to Holocene).
Uses & applications
Historical building stone (notably in Florida), road base material, garden decoration, and as a source of calcium carbonate for agricultural use.
Geological facts
The Castillo de San Marcos in Florida was built from coquina; the stone's porous nature allowed it to absorb cannonball impacts rather than shattering.
Field identification & locations
Identifiable by its visible, poorly sorted shell fragments and high porosity. Found in coastal regions like Florida, the Outer Banks, and Australia (Shark Bay). Collectors look for well-preserved fossil imprints.
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