sedimentary

Coquina / Shelly Limestone

Coquina (Biogenic Limestone)

AI-generated identification · may be incorrect

Hardness: 3-4 (variable), Color: Cream, tan, or grayish-white, Luster: Dull/Earthy, Crystal Structure: Amorphous/Organic remains, Cleavage: None/Irregular, Specific Gravity: Low (highly porous)

Identified April 10, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (variable), Color: Cream, tan, or grayish-white, Luster: Dull/Earthy, Crystal Structure: Amorphous/Organic remains, Cleavage: None/Irregular, Specific Gravity: Low (highly porous)

Formation & geological history

Formed in high-energy marine environments (beaches) during the Holocene or Pleistocene epochs. It consists of mechanically sorted shell fragments cemented together by calcium carbonate precipitation.

Uses & applications

Historically used as building stone (e.g., Castillo de San Marcos) due to its ability to absorb cannon fire. Currently used for decorative landscaping, road gravel, and concrete aggregate.

Geological facts

Coquina is unique because it is soft when first quarried but hardens when exposed to air. Its porous nature allowed it to absorb historical cannonballs rather than shattering like brick or granite.

Field identification & locations

Identify by looking for visible, broken shell fragments and a 'crunchy' texture. It will react and fizz strongly if a drop of vinegar (acid) is applied.