sedimentary
Coquina
Bioclastic Limestone (CaCO3)
Hardness: 2-3 (Mohs scale), Color: tan, cream, or light brown, Luster: dull to earthy, Texture: coarse-grained, clastic with visible shell fragments, Specific Gravity: 2.2-2.4
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Physical properties
Hardness: 2-3 (Mohs scale), Color: tan, cream, or light brown, Luster: dull to earthy, Texture: coarse-grained, clastic with visible shell fragments, Specific Gravity: 2.2-2.4
Formation & geological history
Formed in high-energy marine environments such as beaches where wave action sorts and accumulates shell fragments of mollusks and invertebrates. The shells are then naturally cemented over geological time by calcium carbonate.
Uses & applications
Historically used as a building material for forts and coastal structures; currently used in construction as a road base, in landscaping, and sometimes for ornamental stone.
Geological facts
The Castillo de San Marcos in St. Augustine, Florida, is the most famous structure built from coquina; its porous nature allowed it to absorb cannonball impacts rather than shattering.
Field identification & locations
Identify in the field by its distinct appearance resembling 'glued-together cereal' or shells; it will effervesce (fizz) vigorously when in contact with diluted hydrochloric acid. Common in coastal Florida and North Carolina.
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