sedimentary

Coquina or Fossiliferous Limestone

Biogenic Limestone (Calcite/Aragonite CaCO3)

AI-generated identification · may be incorrect

Hardness: 3 (Mohs scale), Color: tan, grey, or off-white. Luster: dull to earthy. Structure: clastic/fragmental with visible fossil shells and coral. Highly porous and permeable.

Hardness: 3 (Mohs scale), Color: tan, grey, or off-white
Color: tan, grey, or off-white
Luster: dull to earthy

Identified April 8, 2026More sedimentary →

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Physical properties

Hardness: 3 (Mohs scale), Color: tan, grey, or off-white. Luster: dull to earthy. Structure: clastic/fragmental with visible fossil shells and coral. Highly porous and permeable.

Formation & geological history

Formed in high-energy marine environments where shell fragments and coral debris accumulate and are cemented together by calcium carbonate. Most coastal Florida specimens are from the Pleistocene era (approx. 12,000 to 2.5 million years ago).

Uses & applications

Used primarily in landscaping, coastal erosion control (riprap), and historically as a unique building stone for forts and cathedrals due to its ability to absorb cannon fire rather than shatter.

Geological facts

Coquina is famous for its role in the construction of the Castillo de San Marcos in St. Augustine, Florida. Because the rock is porous, it compressed rather than shattered when hit by British cannonballs.

Field identification & locations

Identify by visible shell fragments, coral imprints, and a 'honeycomb' texture. It will fizz when exposed to weak acid (like vinegar). Commonly found in coastal regions, particularly Florida and the Carolinas.