sedimentary

Coquina / Fossiliferous Limestone

Fossiliferous Limestone (Calcite, CaCO3)

AI-generated identification · may be incorrect

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

Identified July 22, 2026More sedimentary →

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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.