sedimentary

Coquina / Fossiliferous Limestone

Biogenic Limestone (Calcium Carbonate - CaCO3)

AI-generated identification · may be incorrect

Hardness: 3-4 (Mohs scale); Color: Tan, brownish-orange, creamy white; Luster: Dull, earthy; Structure: Fragmental/Clastic containing fossil imprints; Cleavage: None; Specific Gravity: 2.3-2.7

Hardness: 3-4 (Mohs scale)
Color: Tan, brownish-orange, creamy white
Luster: Dull, earthy

Identified March 29, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (Mohs scale); Color: Tan, brownish-orange, creamy white; Luster: Dull, earthy; Structure: Fragmental/Clastic containing fossil imprints; Cleavage: None; Specific Gravity: 2.3-2.7

Formation & geological history

Formed in high-energy marine environments where shell fragments and marine debris accumulate and are naturally cemented by calcium carbonate (calcite). These specimens often date from the Cenozoic Era to the present.

Uses & applications

Used historically as a construction material for forts (like Castillo de San Marcos) and homes, as base material for roads, and as a decorative stone in landscaping and fossil collecting.

Geological facts

This specific piece is rich in gastropod (snail-like) and bivalve molds. In historic forts, coquina proved surprisingly effective against cannonballs because the porous rock would compress and absorb the impact rather than shattering.

Field identification & locations

Identify in the field by looking for a rock composed almost entirely of shells or shell molds (negative imprints). Frequently found in coastal regions, particularly Florida, North Carolina, and the Caribbean. It will fizz when exposed to weak acid (vinegar).