Rock Identifier
Fossil shell fragment, likely bivalve or brachiopod (Indeterminate fossilized mollusk/brachiopod; commonly calcite (CaCO₃)) — fossil
fossil

Fossil shell fragment, likely bivalve or brachiopod

Indeterminate fossilized mollusk/brachiopod; commonly calcite (CaCO₃)

AI-generated identification · may be incorrect

Gray-beige, weathered, irregularly curved shell with possible ribbing and a dull to slightly waxy luster; fossil shell material is typically Mohs 3, with calcite cleavage and specific gravity near 2.7. The image is insufficient for confident species identification.

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Physical properties

Gray-beige, weathered, irregularly curved shell with possible ribbing and a dull to slightly waxy luster; fossil shell material is typically Mohs 3, with calcite cleavage and specific gravity near 2.7. The image is insufficient for confident species identification.

Formation & geological history

A marine shell was buried in carbonate sediment and mineralized or recrystallized during diagenesis, commonly in Paleozoic–Cenozoic sedimentary rocks. Exact age cannot be determined visually.

Uses & applications

Primarily a teaching, display, or collecting specimen; calcitic fossil material has little industrial value compared with limestone.

Geological facts

The broad curved form and layered/ridged surface suggest a partial shell rather than an igneous or metamorphic rock. Acid fizzing would support calcite, though testing may damage it.

Field identification & locations

Look for bilateral shell symmetry, growth lines, ribs, hinge structures, and a contrasting sedimentary matrix; common sources include limestone exposures worldwide. Avoid aggressive cleaning or acid tests.

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Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

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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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Porous limestone pebble (Calcite-rich limestone (primarily CaCO₃); exact identification is uncertain from the image) — sedimentary

Porous limestone pebble

Calcite-rich limestone (primarily CaCO₃); exact identification is uncertain from the image

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Weathered fossil bone fragment (identification uncertain)

Fossilized bone; exact taxon and mineral composition cannot be determined from the image

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