fossil
Bivalve Fossil (Internal Mold)
Bivalvia (Phalladomya or similar genus)
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
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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.
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