sedimentary

Fossilized Oyster Shell (Limestone/Coquina)

Crassostrea (Fossilized Bivalve), Calcium Carbonate (CaCO3)

AI-generated identification · may be incorrect

Hardness: 3 (Mohs scale for Calcite); Color: Off-white, grey, tan; Luster: Dull/Earthy to Pearly; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral

Hardness: 3 (Mohs scale for Calcite)
Color: Off-white, grey, tan
Luster: Dull/Earthy to Pearly

Identified June 3, 2026More sedimentary →

Explore Fossilized Oyster Shell (Limestone/Coquina) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 3 (Mohs scale for Calcite); Color: Off-white, grey, tan; Luster: Dull/Earthy to Pearly; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral

Formation & geological history

Formed through the accumulation of organic debris in shallow marine environments during the Cenozoic or Mesozoic eras. Over millions of years, pressure and mineralization convert shells into fossiliferous limestone.

Uses & applications

Used primarily in construction (aggregate, cement making), soil conditioning, and as a component of decorative landscaping rocks.

Geological facts

Fossilized oysters are key indicators of paleo-environments, showing where ancient coastlines and estuaries once existed. In some regions, entire roadbeds are built from shell-rich limestone called Coquina.

Field identification & locations

Identify by visible concentric growth lines and a heavy, stony feel compared to a fresh shell. Found in coastal regions, limestone quarries, and dry creek beds where prehistoric seas once stood.