sedimentary
Coquina
Biogenic Limestone (Calcium Carbonate, CaCO3)
Hardness: 2-3 (Mohs scale); Color: Tan, brownish, or gray; Luster: Dull/Earthy; Structure: Clastic fossil fragments; Porosity: Very high.
- Hardness
- 2-3 (Mohs scale)
- Color
- Tan, brownish, or gray
- Luster
- Dull/Earthy
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Physical properties
Hardness: 2-3 (Mohs scale); Color: Tan, brownish, or gray; Luster: Dull/Earthy; Structure: Clastic fossil fragments; Porosity: Very high.
Formation & geological history
Formed in high-energy marine environments (beaches or barrier islands) where shells are broken by wave action and later cemented together by calcium carbonate.
Uses & applications
Historically used as a building material for forts and homes due to its ability to absorb cannon fire (it compresses rather than shattering). Used today as road base or landscaping stone.
Geological facts
The Castillo de San Marcos in Florida was built of coquina; during battles, cannonballs would sink into the soft stone rather than breaking it.
Field identification & locations
Identify by looking for a mass of visible, broken shell fragments. It will react and fizz strongly when exposed to dilute hydrochloric acid (vinegar).
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