sedimentary

Coquina

Biogenic Limestone (Calcium Carbonate, CaCO3)

AI-generated identification · may be incorrect

Hardness: 2-3 (Mohs). Color: Tan, beige, or white with visible shell fragments. Luster: Dull or earthy. Structure: Granular and poorly consolidated (clastic). High porosity.

Hardness: 2-3 (Mohs)
Color: Tan, beige, or white with visible shell fragments
Luster: Dull or earthy

Identified June 26, 2026More sedimentary →

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Physical properties

Hardness: 2-3 (Mohs). Color: Tan, beige, or white with visible shell fragments. Luster: Dull or earthy. Structure: Granular and poorly consolidated (clastic). High porosity.

Formation & geological history

Formed in high-energy marine shoreline environments where shell fragments and calcified organic debris accumulate. Over time, these are lightly cemented by calcium carbonate from percolating groundwater. Most specimens are relatively young, from the Pleistocene or Holocene epochs.

Uses & applications

Historically used as a building material for fortresses (like Castillo de San Marcos) and homes. Today it is used in road base construction, landscaping, and as a decorative stone.

Geological facts

The name 'coquina' is Spanish for 'little shells.' Because it is soft and porous, it was historically used in military forts because it would absorb the impact of cannonballs rather than shattering like harder stone.

Field identification & locations

Identify it by looking for visible shell fragments that look like they are glued together. It will often fizz when exposed to dilute hydrochloric acid. It is most commonly found along the Atlantic coast from North Carolina down through Florida.