Coquina or Fossiliferous Limestone

Physical Properties

Hardness: 3 (Mohs scale); Color: Tan, gray, or cream-white; Luster: Dull/Earthy; Crystal Structure: Usually microcrystalline calcite with visible macro-fossils; Cleavage: None (fragmented); Specific Gravity: 2.3-2.7

Formation & Geological History

Formed in marine environments through the accumulation of shell fragments, coral debris, and other organic skeletal materials. These are cemented together by calcium carbonate over thousands to millions of years.

Uses & Applications

Historically used as a building material (like the Castillo de San Marcos in Florida), for road base, in the manufacturing of cement, and for decorative landscaping.

Geological Facts

Coquina is unique because it is soft when first quarried but hardens when exposed to air. Its porous nature famously allowed it to absorb the impact of cannonballs during historical sieges rather than shattering.

Field Identification & Locations

Identify in the field by looking for visible shell fragments or small holes (vugs) where organic matter dissolved. It will react and fizz strongly if touched with a drop of vinegar (dilute acid). Commonly found along coastal areas and ancient sea beds.

Identified on: 4/29/2026

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