sedimentary

Coquina Limestone

Coquina (Biogenic Limestone)

Hardness: 3 on Mohs scale (composed predominantly of calcite). Color: Tan, beige, light brown, with white shell fragments. Luster: Earthy, dull, to pearly. Texture: Very coarse, porous, consisting of loosely cemented shell fragments. Cleavage: None.

Hardness: 3 on Mohs scale (composed predominantly of calcite)
Color: Tan, beige, light brown, with white shell fragments
Luster: Earthy, dull, to pearly

Identified July 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in high-energy marine shoreline or beach environments where shell debris from mollusks and invertebrates accumulates rapidly and is weakly cemented by calcium carbonate (calcite).

Uses & applications

Historically used as a building material for forts, seawalls, and structures (e.g., Castillo de San Marcos in Florida) because its soft, porous nature absorbed cannonball impacts rather than shattering. Also used in crushed form for road bases and landscaping.

Geological facts

Coquina is famous for its unique structural resilience; historical stone walls made of coquina absorbed cannon fire like memory foam, making them virtually indestructible to ancient artillery.

Field identification & locations

Easily identified by its oatmeal-like or granola-like appearance composed almost entirely of visible, broken shell fragments. Highly reactive and fizzes strongly when tested with dilute hydrochloric acid.