Rock Identifier
Fossilized bivalve shell or shell-rich limestone (Likely an indeterminate fossil mollusk; calcite/aragonite (CaCO₃), possibly preserved in limestone) — fossil
fossil

Fossilized bivalve shell or shell-rich limestone

Likely an indeterminate fossil mollusk; calcite/aragonite (CaCO₃), possibly preserved in limestone

AI-generated identification · may be incorrect

Gray-green to tan, elongated and strongly ribbed, with an irregular weathered surface and probable shell growth lines. Original shell mineral may be calcite or altered to calcite; hardness about 3, nonmetallic luster, low cleavage, and specific gravity roughly 2.6–2.8.

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Physical properties

Gray-green to tan, elongated and strongly ribbed, with an irregular weathered surface and probable shell growth lines. Original shell mineral may be calcite or altered to calcite; hardness about 3, nonmetallic luster, low cleavage, and specific gravity roughly 2.6–2.8.

Formation & geological history

Most likely a marine mollusk shell mineralized by burial and diagenesis, potentially tens to hundreds of millions of years old; exact age requires locality and preparation details. The surrounding material may be carbonate rock.

Uses & applications

Primarily a collecting, educational, or decorative specimen; carbonate fossil material can also be used as aggregate or limestone feedstock when abundant, though this individual is not industrially significant.

Geological facts

The repeated ridges and tapered outline suggest a shell rather than an igneous or metamorphic rock. Surface holes may represent weathering, dissolution, or bioerosion.

Field identification & locations

Look for bilateral shell symmetry, continuous growth ribs, and a calcitic reaction to dilute hydrochloric acid or vinegar; avoid testing valuable specimens. Common in marine sedimentary formations worldwide, especially limestone and shale exposures.

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Unidentified carbonate-rich concretion with a possible fossil inclusion

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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 (Phylum Echinodermata, Class Crinoidea) — fossil

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

sedimentary
Weathered fossil bone fragment (identification uncertain) (Fossilized bone; exact taxon and mineral composition cannot be determined from the image) — fossil

Weathered fossil bone fragment (identification uncertain)

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

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