fossil

Bivalve Internal Mold Fossil

Steinkern (Bivalvia mold)

Hardness: variable (3-4 if limestone/calcite, 6-7 if silicified); Color: grey to tan with earthy texture; Luster: dull/non-reflective; Shape: asymmetrical oval resembling a heart or shell; No visible external shell material.

Hardness: variable (3-4 if limestone/calcite, 6-7 if silicified)
Color: grey to tan with earthy texture
Luster: dull/non-reflective

Identified July 18, 2026More fossil →

Explore Bivalve Internal Mold Fossil in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Formation & geological history

Formed during the Mesozoic or Cenozoic eras when sediment filled a clam or mussel shell after the animal died. The shell eventually dissolved, leaving a hardened sediment 'cast' of the interior cavity.

Uses & applications

Primarily for educational purposes, paleontological study, and amateur fossil collecting.

Geological facts

These fossils are often called 'heart stones' or 'deer hearts' because their shape can mimic a mammalian heart. In some cultures, they were considered luck charms.

Field identification & locations

Check for concentric growth lines or a symmetrical 'beak' at the hinge point. Frequently found in limestone quarries, coastal cliffs, and riverbeds where sedimentary layers are exposed.

Other fossil specimens

See all

Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

fossil

Sedimentary Outcrop (Sandstone/Shale)

Sedimentary bedrock formation (variable composition)

sedimentary

Chert with Fossil Brachiopod

Microcrystalline Quartz (SiO2) with Calcitic Brachiopod inclusion

sedimentary

Fossiliferous Limestone

Fossiliferous Calcilutite / Biomicrite

sedimentary

Fossilized Crinoid Stem in Limestone

Crinoidea (Class) in Calcium Carbonate (CaCO3) matrix

fossil

Fossiliferous Limestone

Limestone with embedded fossil cross-section

sedimentary