sedimentary
Coquina
Biogenic Limestone (Calcium Carbonate, CaCO3)
Hardness: 2-3 (Mohs scale); Color: Cream, tan, or white; Luster: Dull to earthy; Crystal structure: Amorphous to microcrystalline; Cleavage: None; High porosity.
- Hardness
- 2-3 (Mohs scale)
- Color
- Cream, tan, or white
- Luster
- Dull to earthy
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Physical properties
Hardness: 2-3 (Mohs scale); Color: Cream, tan, or white; Luster: Dull to earthy; Crystal structure: Amorphous to microcrystalline; Cleavage: None; High porosity.
Formation & geological history
Formed in high-energy marine environments (beaches) where waves accumulate shell fragments and coral debris. These fragments are loosely cemented together by calcite. Mostly formed during the Holocene and Pleistocene epochs.
Uses & applications
Used as a construction material (notably in Spanish forts like Castillo de San Marcos), as road base material, and occasionally in landscaping or as a phosphate source.
Geological facts
Coquina is unique because it is soft enough to be quarried easily but becomes stronger over time as it dries. Its porous nature allowed it to absorb cannonball impacts rather than shattering, making it an excellent fortification material.
Field identification & locations
Identify in the field by its visible shell fragments and rough, 'oatmeal-like' texture. It will effervesce (fizz) when exposed to dilute hydrochloric acid. Commonly found along the coastlines of Florida and North Carolina.
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