sedimentary
Coquina
Biogenic Limestone (Calcium Carbonate, CaCO3)
Hardness: 2-3 (Mohs scale); Color: tan, cream, or beige; Luster: earthy; Structure: clastic/bioclasts; Cleavage: none; Porosity: very high
- Hardness
- 2-3 (Mohs scale)
- Color
- tan, cream, or beige
- Luster
- earthy
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Physical properties
Hardness: 2-3 (Mohs scale); Color: tan, cream, or beige; Luster: earthy; Structure: clastic/bioclasts; Cleavage: none; Porosity: very high
Formation & geological history
Formed in high-energy marine environments (beaches) where waves accumulate shell fragments and coral debris, which over time are loosely cemented by calcite. Usually from the Holocene or Pleistocene eras.
Uses & applications
Historical building stone (notably in Florida), road base material, landscaping, and phosphate source for fertilizers.
Geological facts
Famous for its use in the Castillo de San Marcos in St. Augustine, Florida; the rock's porous nature allowed it to absorb cannonball impacts rather than shattering.
Field identification & locations
Identify by its 'oatmeal' appearance consisting entirely of visible shell fragments. Common in coastal areas with high shell accumulation like Florida or Australia.
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