sedimentary
Fossiliferous Limestone (Coquina)
Biogenic Limestone (Calcium Carbonate, CaCO3)
Hardness: 3 (Mohs scale); Color: Cream, tan, or light gray; Luster: Dull/Earthy; Structure: Clastic or bio-clastic texture; Cleavage: None (fractures irregularly); Specific Gravity: 2.3-2.7
- Hardness
- 3 (Mohs scale)
- Color
- Cream, tan, or light gray
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3 (Mohs scale); Color: Cream, tan, or light gray; Luster: Dull/Earthy; Structure: Clastic or bio-clastic texture; Cleavage: None (fractures irregularly); Specific Gravity: 2.3-2.7
Formation & geological history
Formed in warm, shallow marine environments from the accumulation of shell fragments, coral, and organic debris. Over time, these sediments are compressed and cemented together by calcite. This specific specimen appears to be from the Cenozoic era, potentially the Pleistocene or Holocene.
Uses & applications
Used primarily as building stone (historically for forts and coastal structures), aggregate in road construction, and for lime production. It is also a popular specimen for educational purposes and novice fossil collectors.
Geological facts
This specimen contains a clear brachiopod or bivalve shell impression. Coquina was famously used to build the Castillo de San Marcos in Florida; its porous nature allowed the walls to absorb cannonball impacts rather than shattering.
Field identification & locations
Identified in the field by its light color, visible shell fragments, and its reactive nature to hydrochloric acid (it will fizz). Commonly found in coastal areas, particularly Florida, the Caribbean, and along the Gulf of Mexico.
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