sedimentary

Coquina

Coquina Limestone

AI-generated identification · may be incorrect

Hardness: 2-3 (Mohs scale), Color: tan, cream, or off-white, Luster: dull to earthy, Crystal structure: poorly defined calcite crystals within clasts, Specific gravity: 2.2-2.4

Identified May 16, 2026More sedimentary →

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Physical properties

Hardness: 2-3 (Mohs scale), Color: tan, cream, or off-white, Luster: dull to earthy, Crystal structure: poorly defined calcite crystals within clasts, Specific gravity: 2.2-2.4

Formation & geological history

Formed in high-energy marine environments where waves accumulate accumulation of shells, coral fragments, and other invertebrates. Fossil fragments are cemented together by calcium carbonate. Most deposits are relatively young (Pleistocene to Holocene).

Uses & applications

Used as a construction material, for road base, landscape decoration, and historically in the construction of forts (due to its ability to absorb cannonball impacts).

Geological facts

The Castillo de San Marcos in St. Augustine, Florida, was built using coquina. Its porous nature allowed the walls to absorb cannon fire rather than shattering.

Field identification & locations

Identify by looking for visible, often crushed shell fragments and a porous, 'oatmeal-like' texture. It will fizz strongly when in contact with dilute hydrochloric acid due to high calcite content.