Rock Identifier
Fossilized oyster or other bivalve shell (Calcitic bioclast, commonly Ostrea spp. or Exogyra spp.) — fossil
fossil

Fossilized oyster or other bivalve shell

Calcitic bioclast, commonly Ostrea spp. or Exogyra spp.

AI-generated identification · may be incorrect

Composed mainly of calcite (CaCO₃); whitish-gray, dull to slightly pearly, with concentric growth ridges and irregular layered shell structure. Calcite hardness is about Mohs 3, with moderate density and no obvious crystal cleavage in the fossilized shell.

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Physical properties

Composed mainly of calcite (CaCO₃); whitish-gray, dull to slightly pearly, with concentric growth ridges and irregular layered shell structure. Calcite hardness is about Mohs 3, with moderate density and no obvious crystal cleavage in the fossilized shell.

Formation & geological history

A marine bivalve shell mineralized during burial, commonly by recrystallization or cementation; exact age cannot be determined from the photograph and may range from Cretaceous to recent fossil-bearing deposits.

Uses & applications

Primarily a collecting, educational, and decorative specimen; fossil shell limestone is also used for aggregate, cement, and agricultural lime.

Geological facts

The rounded, coiled-looking form and repeated growth bands are characteristic of a thick, cemented oyster-type shell rather than a crystalline mineral.

Field identification & locations

Look for biological growth lines, shell layering, an irregular valve shape, and calcite reaction to dilute hydrochloric acid or vinegar. Oyster fossils occur widely in marine sedimentary rocks worldwide, especially limestone and coastal deposits.

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Likely fossil oyster shell

Fossilized bivalve shell; exact species cannot be identified from the image

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Crinoid Stem Fossil in Matrix

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Fossiliferous limestone (likely a crinoidal or shell-fragment limestone) (Bioclastic limestone, composed chiefly of calcite (CaCO₃)) — sedimentary

Fossiliferous limestone (likely a crinoidal or shell-fragment limestone)

Bioclastic limestone, composed chiefly of calcite (CaCO₃)

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Rounded sedimentary pebble

Likely micritic limestone or calcareous sandstone

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Chert with Fossil Brachiopod

Microcrystalline Quartz (SiO2) with Calcitic Brachiopod inclusion

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