sedimentary
Coquina or Fossilized Shell Fragment
Calcium Carbonate (CaCO3) / Biogenic Limestone
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 More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
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.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone
Arenite
sedimentary
Sandstone (Quartz-rich)
Arenite (SiO2)
sedimentary