fossil

Bivalve Internal Mold Fossil

Steinkern (Mollusca: Bivalvia)

Hardness: 3-4 (calcite/limestone matrix); Color: Tan, brown, and grey; Luster: Dull/Earthy; Structure: Symmetrical heart or teardrop shaped cast showing the internal cavity of a shell.

Hardness: 3-4 (calcite/limestone matrix)
Color: Tan, brown, and grey
Luster: Dull/Earthy

Identified July 17, 2026More fossil →

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Physical properties

Hardness: 3-4 (calcite/limestone matrix); Color: Tan, brown, and grey; Luster: Dull/Earthy; Structure: Symmetrical heart or teardrop shaped cast showing the internal cavity of a shell.

Formation & geological history

Formed during the Mesozoic or Cenozoic eras when sediment filled the empty shell of a dead mollusk. The original shell dissolved over time, leaving a lithified 'internal mold' or steinkern.

Uses & applications

Educational tools, paleontology study, and scientific collecting. Provides insight into ancient marine environments.

Geological facts

These fossils are colloquially known as 'deer hearts' or 'bull hearts' in some regions due to their anatomical shape. They represent a 'negative' space of the original creature.

Field identification & locations

Identify by the distinct bilateral symmetry and growth lines visible on the surface. Commonly found in limestone quarries, stream beds, and coastal sedimentary outcrops.

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