Coquina / Fossiliferous Limestone

Physical Properties

Hardness: 3-4 (Mohs scale); Color: Brown, tan, reddish-brown with white/grey shells; Luster: Dull to earthy; Structure: Clastic fossil fragments; Specific gravity: approx 2.4-2.7.

Formation & Geological History

Formed in high-energy marine or coastal environments where shell fragments and calcified remains of organisms accumulate and are cemented together by calcium carbonate over millions of years.

Uses & Applications

Used as building material, road base, source of lime for agriculture, and as a decorative specimen for fossil collectors.

Geological Facts

Famous for its use in the construction of the Castillo de San Marcos in Florida, where its porous nature allowed it to absorb cannonball impacts rather than shattering.

Field Identification & Locations

Identify by looking for visible shell fragments, spirals, or curved white lines within a matrix. It will react and fizz if a drop of vinegar (weak acid) is applied.

Identified on: 4/24/2026

Mode: Standard