sedimentary
Coquina
Coquina Limestone (CaCO3)
Hardness: 2-3 (Mohs scale), Color: tan, cream, white, or gray-pink, Luster: dull to earthy, Crystal Structure: massive/amorphous appearing due to shell fragments, Cleavage: none, Specific Gravity: 2.3-2.5
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Physical properties
Hardness: 2-3 (Mohs scale), Color: tan, cream, white, or gray-pink, Luster: dull to earthy, Crystal Structure: massive/amorphous appearing due to shell fragments, Cleavage: none, Specific Gravity: 2.3-2.5
Formation & geological history
Formed in high-energy marine environments (beaches or offshore bars) where wave action accumulates shell fragments. The shells are cemented together by Calcium Carbonate over many thousands of years.
Uses & applications
Used as a historical building material (source of lime), in road gravel, for shoreline armoring (revetments), and as decorative landscaping stones.
Geological facts
Famous historic structures like the Castillo de San Marcos in St. Augustine, Florida, were built with coquina because it was so porous it could absorb cannonball fire without shattering.
Field identification & locations
Identify by looking for visible shell fragments or fossils weakly cemented together. It is commonly found along coasts with high mollusk populations like the Atlantic coast of Florida and North Carolina.
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