sedimentary

Coquina

Biogenic Limestone (Calcium Carbonate, CaCO3)

AI-generated identification · may be incorrect

Hardness: 2-3 (Mohs scale); Color: Brown, tan, cream, or greyish-white; Luster: Dull or earthy; Structure: Fragmental/clastic composed of shell debris; Cleavage: None (friable/crumbly); Specific Gravity: 1.5 - 2.4.

Hardness: 2-3 (Mohs scale)
Color: Brown, tan, cream, or greyish-white
Luster: Dull or earthy

Identified April 4, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in high-energy marine environments (beaches) where wave action accumulates broken shells, coral, and other organic debris. Over time, these fragments are naturally cemented together by calcium carbonate. Most deposits are relatively young (Pleistocene to Holocene).

Uses & applications

Used as a historical building material (e.g., Castillo de San Marcos), road base aggregate, landscaping stone, and in the production of lime and cement. It is also a popular specimen for educational fossil collecting.

Geological facts

Coquina is famous for its 'energy-absorbing' quality in military history; during the 17th century, cannonballs fired at coquina forts would sink into the soft walls rather than shattering them. It is the state rock of Florida.

Field identification & locations

Identify it by its distinctive 'oatmeal-like' appearance consisting almost entirely of small shell fragments. It is highly reactive to cold dilute hydrochloric acid (it will fizz). Commonly found along coastal areas in Florida, North Carolina, and Australia.