sedimentary

Coquina

Coquina (Biogenic Limestone / CaCO3)

Hardness: 2-3 (Mohs scale); Color: Tan, brown, or cream-colored; Luster: Dull to earthy; Crystal structure: Amorphous to microcrystalline; Cleavage: None (friable/mechanical); Specific gravity: 1.5 - 2.5 (highly porous).

Hardness: 2-3 (Mohs scale)
Color: Tan, brown, or cream-colored
Luster: Dull to earthy

Identified March 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in high-energy marine shoreline environments where wave action accumulates shell fragments. Over time, these fragments are cemented together by calcium carbonate. Most deposits are relatively young (Pleistocene to Holocene), though some date back to the Jurassic.

Uses & applications

Historically used as a building stone (e.g., Castillo de San Marcos) due to its impact-absorbing properties; currently used as road base, decorative landscaping stone, and in the production of lime and cement.

Geological facts

Because it is composed of loosely cemented shell fragments, it has the unique property of absorbing cannonball impacts rather than shattering, which made it a superior material for colonial-era fortifications in Florida.

Field identification & locations

Identify in the field by its 'oatmeal-like' texture clearly composed of broken sea shells and coral. It is highly reactive (effervesces) with dilute hydrochloric acid. Commonly found along the coastlines of Florida, the Bahamas, and Australia.