sedimentary

Coquina

Biogenic Limestone (Coquina)

Hardness: 2-3 (Mohs scale), Color: tan, buff, or white, Luster: dull/earthy, Structure: clastic/fragmental, Cleavage: N/A, Specific Gravity: 1.5 - 2.5

Identified June 2, 2026More sedimentary →

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Physical properties

Hardness: 2-3 (Mohs scale), Color: tan, buff, or white, Luster: dull/earthy, Structure: clastic/fragmental, Cleavage: N/A, Specific Gravity: 1.5 - 2.5

Formation & geological history

Formed in high-energy marine environments like beaches and barrier islands where shell fragments accumulate and are rapidly cemented by calcium carbonate; typically Holocene or Pleistocene in age.

Uses & applications

Used as a construction material, in road base, as decorative landscaping stone, and historically as a primary building material for coastal fortifications due to its ability to absorb cannon fire.

Geological facts

The Castillo de San Marcos in St. Augustine, Florida, is the most famous structure built of coquina; its porous nature allowed it to absorb cannonball impacts rather than shattering.

Field identification & locations

Identify by its 'oatmeal' or 'shredded wheat' appearance consisting almost entirely of visible, broken shell fragments; commonly found along coastlines of Florida and the Carolinas.