sedimentary
Coquina (Fossiliferous Limestone)
Biogenic Limestone (Calcium Carbonate, CaCO3)
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
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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.
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