Coquina (Limestone)

Physical Properties

Hardness: 3 (Mohs scale), Color: Cream, tan, or white, Luster: Dull/Earthy, Crystal Structure: Amorphous/Biogenic, Porous and friable texture

Formation & Geological History

Formed in high-energy marine environments (beaches/reefs) by the accumulation and mechanical sorting of shell fragments and coral debris, typically from the Holocene or Pleistocene epochs.

Uses & Applications

Used as a historical building material (source of lime), in road construction, landscaping, and as a natural aquarium filter due to high calcium content.

Geological Facts

The Castillo de San Marcos in Florida is famously built from coquina; its porous nature allowed it to absorb cannonball impacts rather than shattering.

Field Identification & Locations

Identify by visible shell fragments, high porosity, and strong effervescence when exposed to dilute hydrochloric acid. Commonly found along coastal areas with significant molluscan life.

Identified on: 5/3/2026

Mode: Standard