fossil
Bivalve Fossil (Internal Mold)
Class Bivalvia (Indeterminate genus)
Hardness: 3-4 (calcitic) or 6-7 (siliceous replacement); Color: brownish-tan, grey, or mottled; Luster: matte/dull; Structure: semicircular or heart-shaped internal cast; Cleavage: none.
- Hardness
- 3-4 (calcitic) or 6-7 (siliceous replacement)
- Color
- brownish-tan, grey, or mottled
- Luster
- matte/dull
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Physical properties
Hardness: 3-4 (calcitic) or 6-7 (siliceous replacement); Color: brownish-tan, grey, or mottled; Luster: matte/dull; Structure: semicircular or heart-shaped internal cast; Cleavage: none.
Formation & geological history
Formed through the fossilization of a prehistoric marine mollusk. The shell filled with sediment which then hardened into stone (a 'steinkern'), while the original shell material typically dissolved or eroded away over millions of years. Common in Mesozoic or Cenozoic strata.
Uses & applications
Scientific study, educational tools, and hobbyist collecting.
Geological facts
Internal molds like this are often nicknamed 'deer hearts' or 'bulls hearts' because of their suggestive heart-like shape when both valves are preserved together. Bivalves have existed since the Cambrian period.
Field identification & locations
Identify by looking for a characteristic symmetrical 'hinge' area and a rounded, convex shape that resembles a clam shell without the outer texture. Commonly found in limestone outcrops, riverbeds, and coastal areas.
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