sedimentary
Coquina / Fossiliferous Limestone
Calcareous bioclastic sedimentary rock (CaCO3)
Hardness: 3 (Mohs scale); Color: Cream, white, or light tan; Luster: Dull/Earthy; Structure: Porous, clastic with visible fossil fragments; Cleavage: None (fractures irregularly).
- Hardness
- 3 (Mohs scale)
- Color
- Cream, white, or light tan
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3 (Mohs scale); Color: Cream, white, or light tan; Luster: Dull/Earthy; Structure: Porous, clastic with visible fossil fragments; Cleavage: None (fractures irregularly).
Formation & geological history
Formed in high-energy marine environments (beaches) where waves accumulate shell fragments, coral, and debris. Over time, these are cemented together by calcium carbonate. Most specimens found on beaches today are from the Holocene or Pleistocene epochs.
Uses & applications
Historically used as building stone (e.g., Castillo de San Marcos in Florida). Today used as road base material, decorative landscaping gravel, and for aquarium decoration.
Geological facts
Coquina is unique because it is soft when first quarried but hardens upon exposure to air. This property allowed it to absorb cannonball impacts during historical battles rather than shattering like brick or granite.
Field identification & locations
Identify by looking for a 'honeycomb' or 'sponge' appearance made entirely of shell fragments. It will react and fizz if a drop of vinegar (weak acid) is applied. Commonly found along the Atlantic coast of Florida and the Carolinas.
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