Rock Identifier
Polished fossil shell fragment (Likely fossilized bivalve shell; mineralized aragonite/calcite (exact taxon indeterminate)) — fossil
fossil

Polished fossil shell fragment

Likely fossilized bivalve shell; mineralized aragonite/calcite (exact taxon indeterminate)

AI-generated identification · may be incorrect

Cream, gray, and brown banding follows curved shell growth lines; has a pearly to dull luster, layered fibrous texture, and irregular fracture. Hardness is approximately 3–4 Mohs if calcitic, or 3.5–4.5 if aragonitic; specific gravity about 2.6–2.9.

Identified More fossil →
Explore Polished fossil shell fragment in the encyclopedia →

Identify your own rocks.

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

App StoreGoogle Play

Physical properties

Cream, gray, and brown banding follows curved shell growth lines; has a pearly to dull luster, layered fibrous texture, and irregular fracture. Hardness is approximately 3–4 Mohs if calcitic, or 3.5–4.5 if aragonitic; specific gravity about 2.6–2.9.

Formation & geological history

Originally formed as a mollusk shell in marine sediment, then buried and partially mineral-replaced during diagenesis. Its geological age cannot be determined from the photograph and may range from Paleozoic to Cenozoic.

Uses & applications

Used as a fossil specimen, paperweight, or decorative polished stone; scientifically valuable chiefly for identification and paleoenvironmental study.

Geological facts

The parallel bands are shell growth increments rather than mineral crystals. Polishing reveals crossed shell layers and can make fossil material resemble banded agate or petrified wood.

Field identification & locations

Look for curved concentric growth lines, shell-layer structure, and possible hinge or rib features; acid testing should be avoided or done cautiously because calcite may effervesce. Common in marine sedimentary formations 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