sedimentary
Coquina / Fossiliferous Limestone
Fossiliferous Calcarenite (Calcium carbonate, CaCO3)
Hardness: 3-4 (Mohs scale); Color: cream, tan, or grey; Luster: dull to earthy; Structure: clastic/biogenic with visible shell fragments and vugs (holes); Cleavage: none.
- Hardness
- 3-4 (Mohs scale)
- Color
- cream, tan, or grey
- Luster
- dull to earthy
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Physical properties
Hardness: 3-4 (Mohs scale); Color: cream, tan, or grey; Luster: dull to earthy; Structure: clastic/biogenic with visible shell fragments and vugs (holes); Cleavage: none.
Formation & geological history
Formed in high-energy marine environments (beaches or shallow reefs) where shell fragments and coral debris accumulate. Over time, these are compacted and cemented by calcite. Many specimens date from the Pleistocene or Holocene epochs.
Uses & applications
Historically used as a building material for forts and colonial structures due to its shock-absorbent nature. Today used in construction gravel, landscaping, and as a calcium source in animal feed.
Geological facts
Famous for its role in the Spanish colonial architecture of Florida; the Castillo de San Marcos survived cannon fire because the soft, porous stone absorbed the impacts rather than shattering.
Field identification & locations
Identified by the presence of numerous small holes and visible shell fragments. In the field, look for 'honeycomb' textures on coastal outcrops. Common in Florida, North Carolina, and coastal Australia.
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