sedimentary

Coquina

Bioclastic Limestone

AI-generated identification · may be incorrect

Hardness: 3 (Mohs scale), Color: tan, gray, or cream-colored, Luster: dull to earthy, Structure: poorly cemented fragments of shells and coral, Cleavage: none (irregular fracture), Specific Gravity: 2.3-2.5

Identified March 23, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in high-energy marine environments like beaches and barrier islands where wave action accumulates sand-sized shell fragments. Most surficial deposits date from the Pleistocene or Holocene epochs.

Uses & applications

Used primarily in construction for building stone or roadbed material. In the past, it was used for fortification walls due to its ability to absorb cannon fire rather than shatter.

Geological facts

The Castillo de San Marcos in Florida is the most famous structure built from coquina; it proved indestructible against British naval cannons in 1702 because the soft rock compressed rather than splintering.

Field identification & locations

Easily identified by its 'breakfast cereal' appearance of visible, broken shell fragments. Commonly found along the Atlantic coast of Florida and the Carolinas.