sedimentary
Coquina
Biogenic Limestone
Hardness: 2-3 (Mohs scale), Color: tan, yellow, grayish-white, Luster: dull to earthy, Crystal Structure: amorphous or microcrystalline (calcium carbonate), Cleavage: none, Specific Gravity: 1.5-2.0 (porous and light)
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Physical properties
Hardness: 2-3 (Mohs scale), Color: tan, yellow, grayish-white, Luster: dull to earthy, Crystal Structure: amorphous or microcrystalline (calcium carbonate), Cleavage: none, Specific Gravity: 1.5-2.0 (porous and light)
Formation & geological history
Formed from the accumulation and biochemical cementation of shells, coral fragments, and other marine invertebrates in high-energy littoral (beach) environments. Usually relatively young, dating from the Pleistocene to Holocene epochs.
Uses & applications
Historically used as a building stone (notable in Florida fortifications like Castillo de San Marcos) because it absorbs cannon fire without shattering. Also used for driveway gravel, landscape stone, and as a source of calcium in agriculture.
Geological facts
The name 'coquina' is Spanish for 'small shell'. Unlike harder stones, coquina's porous nature allows it to condense when struck by projectiles rather than fracturing, making it an excellent defensive building material.
Field identification & locations
Identify by its coarse, 'oatmeal-like' texture clearly consisting of crushed shell fragments. Found along coastlines, particularly in Florida, the Carolinas, and Australia. Test with dilute hydrochloric acid; it will fizz vigorously.
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