sedimentary
Coquina Limestone (Fossiliferous Limestone)
Calcareous bioclastic sedimentary rock (CaCO3)
Hardness: 3 (Mohs scale); Color: tan, buff, or light grey; Luster: dull to earthy; Structure: poorly consolidated to cemented shells; Specific Gravity: 2.3–2.6.
- Hardness
- 3 (Mohs scale)
- Color
- tan, buff, or light grey
- Luster
- dull to earthy
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Physical properties
Hardness: 3 (Mohs scale); Color: tan, buff, or light grey; Luster: dull to earthy; Structure: poorly consolidated to cemented shells; Specific Gravity: 2.3–2.6.
Formation & geological history
Formed in high-energy marine environments like shorelines where shell debris accumulates in thick deposits. Over time, chemical precipitates cement the organic fragments together. Most common in recent geological epochs like the Pleistocene.
Uses & applications
Used primarily in construction for building stone and road base material. Historically used for fortresses due to its ability to absorb cannon fire. Crushed into aggregate or used as a calcium source in agriculture.
Geological facts
The Castillo de San Marcos in Florida was built from coquina; the stone was so soft it absorbed cannonballs rather than shattering, making the fort nearly invincible for its time.
Field identification & locations
Identify by its coarse, 'oatmeal-like' texture of visible shell fragments. Found commonly along the coastal southeastern United States (especially Florida and the Carolinas) and other worldwide coastlines with high carbonate activity.
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