sedimentary

Coquina or Fossilized Shell Fragment

Calcium Carbonate (CaCO3) / Biogenic Limestone

AI-generated identification · may be incorrect

Hardness: 3 (Mohs scale), Color: White to off-white, Luster: Dull to pearly, Structure: Corrugated/ridged texture from bivalve shell, Cleavage: None (conchoidal fracture when broken)

Identified May 26, 2026More sedimentary →

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Physical properties

Hardness: 3 (Mohs scale), Color: White to off-white, Luster: Dull to pearly, Structure: Corrugated/ridged texture from bivalve shell, Cleavage: None (conchoidal fracture when broken)

Formation & geological history

Formed by the accumulation of biochemical remains (shells) of marine organisms. Over time, these fragments undergo lithification to become sedimentary rock. This specimen appears to be a weathered fragment of a modern or Holocene-era shell.

Uses & applications

Used primarily in construction (road base), as a source of lime, in beach restoration, and as landscaping material. Historically used as a building stone (e.g., Castillo de San Marcos).

Geological facts

The word 'coquina' is Spanish for 'tiny shell.' It is a unique rock because it is porous and soft when first quarried but hardens significantly upon exposure to air. This specific fragment shows the distinctive ribbing of a scallop or similar bivalve.

Field identification & locations

Identify by its light color, ridged texture, and reaction (fizzing) when exposed to a drop of vinegar or mild acid. Commonly found along coastal beaches and in shallow marine sedimentary deposits.