sedimentary
Coquina / Fossiliferous Limestone
Fossiliferous Limestone (Calcite, CaCO3)
Hardness: 3 on Mohs scale; Color: Gray, tan, and off-white; Luster: Dull to earthy; Texture: Bioclastic, packed with visible shell fragments and crinoid/brachiopod debris; Specific gravity: 2.5-2.7
- Hardness
- 3 on Mohs scale
- Color
- Gray, tan, and off-white
- Luster
- Dull to earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: Gray, tan, and off-white; Luster: Dull to earthy; Texture: Bioclastic, packed with visible shell fragments and crinoid/brachiopod debris; Specific gravity: 2.5-2.7
Formation & geological history
Formed in warm, shallow marine environments where shell fragments, coral, and microfossils accumulated on the seafloor and were compacted and cemented over time by calcite precipitation.
Uses & applications
Used historically as a building stone (such as in coastal fortifications like Castillo de San Marcos in Florida), as an aggregate in construction, in cement manufacturing, and as decorative landscape stone.
Geological facts
Coquina and fossiliferous limestones are remarkable because they are made almost entirely of the ancient skeletal remains of marine organisms. Coquina is famous for being able to absorb cannonball impacts due to its porous structure.
Field identification & locations
Identify by looking for densely packed, visible shell fragments or crinoid stems that react vigorously (effervesce) with dilute hydrochloric acid. Commonly found along present and ancient coastal regions, river beds, and limestone quarries.
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