fossil

Fossilized oyster shell

Bivalve mollusk fossil, likely Gryphaea or Exogyra; calcite (CaCO₃) shell material

AI-generated identification · may be incorrect

Hardness about 3 on the Mohs scale; off-white to gray, irregularly folded shell with dull to pearly luster and layered fibrous texture. The specimen retains a strongly curved, thick valve and pronounced growth ridges.

Identified September 21, 2026More fossil →

Explore Fossilized oyster shell in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Formation & geological history

A marine bivalve shell was buried in sediment and mineralized, commonly during the Jurassic or Cretaceous Periods; the exact age cannot be determined from the image alone. Calcite replaced or filled the original aragonitic shell during diagenesis.

Uses & applications

Primarily a teaching, display, and collecting specimen; comparable fossil oysters are also used in educational exhibits and decorative pieces. It has no meaningful industrial value as an individual specimen.

Geological facts

The strongly curled, thick shell resembles an gryphaeid oyster, often informally called a “devil’s toenail.” Its asymmetrical shape reflects growth attached to or resting on seafloor sediment.

Field identification & locations

Identify it by the single thick, curved valve, concentric growth lines, and shell-like ribbing; dilute acid may weakly fizz on exposed calcite. Common examples occur in Jurassic marine rocks of Europe and North America.