sedimentary
Coquina
Coquina Limestone
Hardness: 2-3 (Mohs scale), Color: tan, cream, or off-white, Luster: dull to earthy, Crystal structure: poorly defined calcite crystals within clasts, Specific gravity: 2.2-2.4
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Physical properties
Hardness: 2-3 (Mohs scale), Color: tan, cream, or off-white, Luster: dull to earthy, Crystal structure: poorly defined calcite crystals within clasts, Specific gravity: 2.2-2.4
Formation & geological history
Formed in high-energy marine environments where waves accumulate accumulation of shells, coral fragments, and other invertebrates. Fossil fragments are cemented together by calcium carbonate. Most deposits are relatively young (Pleistocene to Holocene).
Uses & applications
Used as a construction material, for road base, landscape decoration, and historically in the construction of forts (due to its ability to absorb cannonball impacts).
Geological facts
The Castillo de San Marcos in St. Augustine, Florida, was built using coquina. Its porous nature allowed the walls to absorb cannon fire rather than shattering.
Field identification & locations
Identify by looking for visible, often crushed shell fragments and a porous, 'oatmeal-like' texture. It will fizz strongly when in contact with dilute hydrochloric acid due to high calcite content.
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