sedimentary
Coquina / Fossiliferous Limestone
Fossiliferous Limestone / CaCO3
Hardness 3 (Mohs scale), tan to light brown color with shell fragment textures, vitreous to dull luster, biogenic sedimentary structure, reacts with dilute hydrochloric acid.
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Physical properties
Hardness 3 (Mohs scale), tan to light brown color with shell fragment textures, vitreous to dull luster, biogenic sedimentary structure, reacts with dilute hydrochloric acid.
Formation & geological history
Formed in shallow marine, intertidal, or coastal environments through the accumulation, compaction, and cementation of shell fragments and marine organism remains.
Uses & applications
Used historically as building stone (e.g., coastal fortifications), crushed stone for gravel and roads, soil conditioner, and ornamental beach rock.
Geological facts
Coquina is famous for its use in constructing Castillo de San Marcos in St. Augustine, Florida, because its soft texture absorbed cannonball impacts rather than shattering.
Field identification & locations
Easily identified in coastal or riverbed zones by coarse shell fragments cemented together by calcium carbonate or fine sand matrix.
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