fossil

Bivalve Fossil (Internal Mold)

Bivalvia (Phalladomya or similar genus)

AI-generated identification · may be incorrect

Hardness: 3-4 (calcite); Color: Grayish-tan, earthy; Luster: Dull to pearly; Structure: Bilateral symmetry with growth lines; Cleavage: None (conchoidal fracture if broken)

Hardness: 3-4 (calcite)
Color: Grayish-tan, earthy
Luster: Dull to pearly

Identified July 17, 2026More fossil →

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Physical properties

Hardness: 3-4 (calcite); Color: Grayish-tan, earthy; Luster: Dull to pearly; Structure: Bilateral symmetry with growth lines; Cleavage: None (conchoidal fracture if broken)

Formation & geological history

Formed during the Mesozoic or Cenozoic eras when sediment filled a bivalve shell and hardened into rock, while the original shell material later dissolved, leaving a 'steinkern' or internal cast.

Uses & applications

Educational tools, paleontology study, and private fossil collections.

Geological facts

These 'heart-shaped' fossils were once thought by various cultures to be petrified hearts or 'thunderstones'. They represent marine mollusks that once lived in shallow sea floors.

Field identification & locations

Identified by their distinctive shell shape and symmetrical growth ridges. Commonly found in limestone beds, chalk cliffs, or creek banks where sedimentary layers are exposed.