sedimentary

Coquina

Bioclastic Limestone (composed primarily of Calcium Carbonate / CaCO3)

AI-generated identification · may be incorrect

Hardness: 2-3 Mohs; Color: White, cream, tan, or grey; Luster: Dull to earthy; Structure: Granular and porous with visible shell fragments; Cleavage: None (conchoidal fracture when broken); Specific Gravity: 2.3-2.5.

Hardness: 2-3 Mohs
Color: White, cream, tan, or grey
Luster: Dull to earthy

Identified March 22, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in high-energy marine environments (beaches or shallow reefs) where shells or coral fragments accumulate. Geologically, these range from the Pleistocene (recent) to older Cenozoic eras.

Uses & applications

Historically used as a building material for forts and coastal structures (notably St. Augustine, FL); also used as gravel, road base, or source of lime for agriculture.

Geological facts

Coquina is uniquely soft when first quarried but hardens upon exposure to air. This porosity allowed it to absorb cannonballs rather than shattering, making it an ideal fortification material.

Field identification & locations

Identify by looking for poorly cemented collections of broken clam shells or coral debris that react with dilute hydrochloric acid. It is commonly found along the Atlantic coast of Florida and North Carolina.