sedimentary

Coquina Limestone

Biogenic Limestone (Calcium Carbonate, CaCO3)

AI-generated identification · may be incorrect

Hardness: 3 (Mohs scale); Color: Cream, tan, or grayish-white; Luster: Dull or earthy; Structure: Fragmental/Clastic composed of shells; Cleavage: None (friable/crumbly); Specific gravity: 2.3 to 2.5.

Hardness: 3 (Mohs scale)
Color: Cream, tan, or grayish-white
Luster: Dull or earthy

Identified March 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in high-energy marine environments (beaches or shallow reefs) where shell fragments accumulate and are naturally cemented by calcite. Most common in Holocene and Pleistocene deposits.

Uses & applications

Historically used for building fortifications (it absorbs cannonballs without shattering) and decorative architecture. Today used as road base material and landscaping stone.

Geological facts

Famous for being the primary building material of the Castillo de San Marcos in Florida, which resisted British attacks for decades because the soft coquina absorbed projectiles.

Field identification & locations

Identify in the field by looking for visible fossil shell fragments or whole shells held together with minimal cement. Found in coastal areas like Florida or North Carolina. It will effervesce (fizz) under weak acid like vinegar.