Rock Identifier
Fossil Bivalve / Ostreid Shell (Hag Stone / Perforated Pebble) (Phylum Mollusca, Class Bivalvia) — fossil
fossil

Fossil Bivalve / Ostreid Shell (Hag Stone / Perforated Pebble)

Phylum Mollusca, Class Bivalvia

AI-generated identification · may be incorrect

Hardness: 3-4 (Calcite/Aragonite); Color: Light grey to white; Luster: Dull to vitreous; Structure: Crystalline calcium carbonate with preserved organic shell matrix.

Hardness
3-4 (Calcite/Aragonite)
Color
Light grey to white
Luster
Dull to vitreous
Identified More fossil →
Explore Fossil Bivalve / Ostreid Shell (Hag Stone / Perforated Pebble) in the encyclopedia →

Identify your own rocks.

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

App StoreGoogle Play

Physical properties

Hardness: 3-4 (Calcite/Aragonite); Color: Light grey to white; Luster: Dull to vitreous; Structure: Crystalline calcium carbonate with preserved organic shell matrix.

Formation & geological history

Formed in ancient marine environments (shallow seas or coastal areas), where carbonate shells accumulated in sediment and underwent lithification and fossilization over millions of years.

Uses & applications

Used for geological education, fossil collecting, and historically regarded as folk talismans or 'hag stones' for protection.

Geological facts

Many naturally tumbled beach pebbles that feature distinct shapes or inclusions are preserved shells or fossil fragments that have been smoothed by wave action.

Field identification & locations

Found along beaches, riverbeds, and limestone-rich sedimentary formations. Identified by characteristic shell morphology and reaction to dilute hydrochloric acid (effervescence).

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