sedimentary

Coquina

Biogenic Limestone (Calcium Carbonate, CaCO3)

AI-generated identification · may be incorrect

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

Identified April 3, 2026More sedimentary →

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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.