fossil

Fossil oyster shell

Ostrea or Exogyra sp. (identification uncertain)

AI-generated identification · may be incorrect

A biogenic calcite shell fossil with strongly layered, irregular growth folds and a thick, curved form. Calcite hardness is about 3 Mohs, with dull to pearly luster; the original shell may be partly replaced or coated by limestone/mineral crust.

Identified August 25, 2026More fossil →

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Physical properties

Formation & geological history

Formed by an oyster-like bivalve in a marine environment, then buried and fossilized through mineral preservation or replacement. Exact age cannot be determined from the photograph; similar fossils range from Mesozoic to Cenozoic strata.

Uses & applications

Primarily a collector’s specimen and teaching material; fossil shells can also be used decoratively, though this example is not suitable as gemstone material.

Geological facts

The irregular layered structure reflects successive shell-growth episodes rather than crystal faces. Oyster fossils commonly preserve concentric growth lines and a strongly curved, cemented attachment valve.

Field identification & locations

Identify it by the unmistakable shell outline, concentric growth laminations, and calcitic reaction to dilute hydrochloric acid or vinegar. Common in marine limestone and coastal sedimentary formations worldwide; avoid acids if preservation is important.