fossil

Fossil oyster shell

Exogyra sp. or a related fossil oyster; largely calcitic shell (CaCO₃)

AI-generated identification · may be incorrect

Hardness about 3 Mohs; irregular, layered shell with pearly to dull luster, white, cream, tan, gray, and brown staining. It shows curved growth lamellae and possible calcite recrystallization rather than a crystalline rock texture.

Identified August 19, 2026More fossil →

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Physical properties

Formation & geological history

A marine bivalve shell preserved in carbonate sediment, later lithified and variably mineralized or weathered. Exact geological age cannot be determined from the image; fossil oysters range from Mesozoic to Cenozoic deposits.

Uses & applications

Primarily a teaching, display, and collecting specimen; polished or stabilized pieces may be used decoratively. It has little industrial value compared with limestone or shell aggregate.

Geological facts

The strongly layered, asymmetrical valve and oyster-like growth form are characteristic of fossil oysters. Brown and yellow colors commonly result from iron-oxide staining or silica/calcite alteration.

Field identification & locations

Identify by the unmistakable shell growth ribs, nacreous layers, and irregular oyster form; acid may weakly fizz on exposed calcite. Common in marine limestone, chalk, and coastal sedimentary formations worldwide.