sedimentary

Coquina

Biogenic Limestone (Coquina)

Hardness: 2-3 (Mohs). Color: Tan, white, or light brown. Luster: Dull to earthy. Crystal structure: Amorphous/microcrystalline calcite. Cleavage: None. Specific Gravity: 2.3-2.5. Highly porous and composed of visible shell fragments.

Hardness: 2-3 (Mohs)
Color: Tan, white, or light brown
Luster: Dull to earthy

Identified July 18, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in high-energy marine environments (beaches) where waves winnow away fine sediment, leaving behind sorted shells and coral fragments that are loosely cemented together by calcite. Mostly Holocene to Pleistocene in age.

Uses & applications

Historically used as a building stone (e.g., Castillo de San Marcos), road base material, and in landscaping or decorative masonry. Its porosity makes it excellent for absorbing cannon fire.

Geological facts

The word 'coquina' is Spanish for 'little shells' or 'cockles'. Because it is so porous, it was used in fortifications because it would absorb cannonballs rather than shattering like harder stones.

Field identification & locations

Identify by looking for a 'oatmeal-like' texture made entirely of tiny sea shells and grit. Commonly found along the Atlantic coast of Florida and in coastal North Carolina.