sedimentary

Coquina (Fossiliferous Limestone)

Biogenic Limestone (Calcium Carbonate, CaCO3)

AI-generated identification · may be incorrect

Hardness: 3 (Mohs scale); Color: Brown, tan, cream; Luster: Dull/Earthy; Structure: Clastic fossil fragments (bioclastic); Cleavage: None; Specific Gravity: 2.3–2.6.

Hardness: 3 (Mohs scale)
Color: Brown, tan, cream
Luster: Dull/Earthy

Identified April 11, 2026More sedimentary →

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Physical properties

Hardness: 3 (Mohs scale); Color: Brown, tan, cream; Luster: Dull/Earthy; Structure: Clastic fossil fragments (bioclastic); Cleavage: None; Specific Gravity: 2.3–2.6.

Formation & geological history

Formed in high-energy marine environments (coastal/beach zones) where sea shells and coral debris accumulate and are cemented together by calcium carbonate. Most deposits are from the Pleistocene or Holocene epochs.

Uses & applications

Historical building material for fortifications, road base material, landscaping, and as a source of lime for agriculture.

Geological facts

Famous for its use in the construction of the Castillo de San Marcos in St. Augustine, Florida. It is unique because it is 'self-healing'; cannonballs would sink into the soft rock rather than shattering it.

Field identification & locations

Identify in the field by its 'granola-like' appearance made of visible shell fragments. It will react and fizz strongly when exposed to cold dilute hydrochloric acid (HCl). Found in coastal regions like Florida, North Carolina, and Australia.