Coquina

Physical Properties

Hardness: 3 (variable), Color: White to tan/brownish, Luster: Dull/earthy, Structure: Highly porous and composed of fragmented shells/skeletons, Specific Gravity: Low (feels light).

Formation & Geological History

Formed in high-energy marine environments where shell fragments and coral debris are broken up by wave action and later cemented together by calcium carbonate.

Uses & Applications

Used primarily in construction for roads and buildings, particularly historical architecture in Florida and the Caribbean. It was historically used for fortifications because its soft nature could absorb cannonballs.

Geological Facts

The Castillo de San Marcos in St. Augustine, Florida, was built from coquina; the stone's porous nature allowed it to 'swallow' cannonballs rather than shattering.

Field Identification & Locations

Identify by its 'granola break' appearance, lack of organized bedding, and presence of visible shell fragments. Commonly found along shorelines and coastal plains.

Identified on: 5/11/2026

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