sedimentary

Coquina or Fossiliferous Limestone

Fossiliferous Limstone (CaCO3)

Hardness: 3-4 (Mohs scale); Color: White, cream, tan; Luster: Dull to earthy; Crystal structure: Hexagonal/trigonal (as calcite); Cleavage: Perfect rhombohedral in calcite crystals; Specific gravity: 2.7

Hardness: 3-4 (Mohs scale)
Color: White, cream, tan
Luster: Dull to earthy

Identified June 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in high-energy marine environments where shell fragments accumulate rapidly and are cemented together by calcium carbonate. Common in coastal areas.

Uses & applications

Used in construction (historical buildings), as a source of lime for agriculture, road base material, and decorative landscaping.

Geological facts

One of the most famous uses of coquina is in the construction of the Castillo de San Marcos in St. Augustine, Florida; the rock is surprisingly effective at absorbing cannon fire because it is relatively soft and compressible.

Field identification & locations

Identify by looking for visible shell fragments or fossils cemented together; it will effervesce (fizz) vigorously when touched with weak acid (like vinegar). Commonly found on beaches and in coastal rock formations.

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