sedimentary

Coquina

Coquina (Bioclastic Calcarenite)

Hardness: 3 (Mohs scale); Color: Tan, beige, or white; Luster: Dull/Earthy; Crystal structure: Amorphous to microcrystalline calcite; Cleavage: None (friable texture); Specific gravity: 1.2 to 2.5.

Hardness: 3 (Mohs scale)
Color: Tan, beige, or white
Luster: Dull/Earthy

Identified January 25, 2026More sedimentary →

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Physical properties

Hardness: 3 (Mohs scale); Color: Tan, beige, or white; Luster: Dull/Earthy; Crystal structure: Amorphous to microcrystalline calcite; Cleavage: None (friable texture); Specific gravity: 1.2 to 2.5.

Formation & geological history

Formed in high-energy marine environments (like beaches and barrier islands) where shell fragments accumulate and are cemented together by calcium carbonate over hundreds to thousands of years; age varies from Pleistocene to Holocene.

Uses & applications

Used primarily in construction for paving stones, roadbase material, and historical building blocks; also used in landscaping and as a source of lime for agriculture.

Geological facts

The Castillo de San Marcos in Florida is a famous fortress built entirely of coquina; it was chosen because the porous rock absorbed the energy of cannonballs rather than shattering.

Field identification & locations

Identify in the field by its 'oatmeal-like' appearance and visible shell fragments. Found extensively along the Atlantic coasts of Florida and the Carolinas. Collectors should check for reactivity; it will effervesce strongly when exposed to a drop of weak acid (like vinegar).