Rock Identifier
Fossilized bivalve shell (Calcitic or aragonitic mollusk shell, commonly Bivalvia; exact species indeterminate) — fossil
fossil

Fossilized bivalve shell

Calcitic or aragonitic mollusk shell, commonly Bivalvia; exact species indeterminate

AI-generated identification · may be incorrect

Hardness about 3–4 Mohs; cream-white, porous, dull to weakly lustrous, with layered shell structure and a pronounced hinge/valve form. Composition is chiefly calcium carbonate (CaCO₃), commonly calcite after diagenetic replacement.

Identified More fossil →
Explore Fossilized bivalve shell in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App StoreGoogle Play

Physical properties

Hardness about 3–4 Mohs; cream-white, porous, dull to weakly lustrous, with layered shell structure and a pronounced hinge/valve form. Composition is chiefly calcium carbonate (CaCO₃), commonly calcite after diagenetic replacement.

Formation & geological history

A marine bivalve shell was buried in sediment and mineralized or preserved during diagenesis; age cannot be determined from the image and may range from Paleozoic to Recent. The apparent split and paired-valve shape are consistent with a shell fossil, though a modern worn shell is also possible.

Uses & applications

Primarily used for education and collecting; crushed shell can serve as calcium feed, soil amendment, or aggregate, but this specimen has little industrial value.

Geological facts

The central hinge region and opposing convex valves are characteristic of bivalves. Surface pores and brown mineral staining commonly reflect weathering and iron-oxide-rich sediment.

Field identification & locations

Look for bilateral valve symmetry, hinge teeth or ligament features, growth lines, and carbonate effervescence in dilute hydrochloric acid; a modern shell may retain nacre or organic layers. Common in marine limestones, beaches, and fossil beds worldwide.

More like this

Other fossil specimens

Probable fossil-bearing rock or mineral concretion (Unidentified carbonate-rich concretion with a possible fossil inclusion) — fossil

Probable fossil-bearing rock or mineral concretion

Unidentified carbonate-rich concretion with a possible fossil inclusion

fossil
Likely fossil oyster shell (Fossilized bivalve shell; exact species cannot be identified from the image) — fossil

Likely fossil oyster shell

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

fossil
Crinoid Stem Fossil in Matrix (Phylum Echinodermata, Class Crinoidea) — fossil

Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

fossil
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
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

fossil