Coquina
“A fortress of shells”
Sedimentary
Coquina is a sedimentary rock composed almost entirely of loosely cemented shell fragments, coral pieces, and other biological debris. Despite its fragile appearance, its porous nature gives it a surprising property in construction.
Composition
calcite (from shells), aragonite, bioclastic fragments
Where Found
St. Augustine (Florida, USA), Brazil, Australia, North Carolina (USA)
Mohs Hardness
2-4
Fun Fact
Castillo de San Marcos in St. Augustine, Florida, was built from coquina — and cannonballs simply sank into the spongy rock rather than shattering it.
Test Your Knowledge
In what type of depositional environment does coquina typically form?
Related Specimens
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