Rock Identifier
Bivalve Fossil (Clam) (Class Bivalvia (e.g., Mercenaria or similar genus)) — fossil
fossil

Bivalve Fossil (Clam)

Class Bivalvia (e.g., Mercenaria or similar genus)

AI-generated identification · may be incorrect

Hardness: 3-4 (Calcite/Aragonite replacement), Color: Tan to grey, Luster: Dull/Earthy, Crystal Structure: Typically microcrystalline calcite replacement of original shell calcium carbonate, Shape: Symmetric valves with distinct hinge line.

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Physical properties

Hardness: 3-4 (Calcite/Aragonite replacement), Color: Tan to grey, Luster: Dull/Earthy, Crystal Structure: Typically microcrystalline calcite replacement of original shell calcium carbonate, Shape: Symmetric valves with distinct hinge line.

Formation & geological history

Formed through permineralization or recrystallization in marine or freshwater sedimentary environments. The soft tissue decays, leaving the shell to be buried by sediment and eventually lithified. Geological age ranges from the Cambrian to the present.

Uses & applications

Educational tools, paleontology study, hobbyist collecting, and sometimes used in decorative mosaics or jewelry if highly silicified.

Geological facts

Bivalves are one of the most successful groups of mollusks. Some fossilized clams can grow to massive sizes (like the Giant Clam), while others provide crucial data for dating sedimentary rock layers.

Field identification & locations

Identify by looking for bilateral symmetry between two shells (valves) and a visible hinge line (umbo). Commonly found in limestone, shale, or sandstone outcrops near ancient coastlines.

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Probable fossil-bearing rock or mineral concretion

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)

sedimentary
Rounded sedimentary pebble (Likely micritic limestone or calcareous sandstone) — sedimentary

Rounded sedimentary pebble

Likely micritic limestone or calcareous sandstone

sedimentary
Chert with Fossil Brachiopod (Microcrystalline Quartz (SiO2) with Calcitic Brachiopod inclusion) — sedimentary

Chert with Fossil Brachiopod

Microcrystalline Quartz (SiO2) with Calcitic Brachiopod inclusion

sedimentary