Rock Identifier
Bivalve Fossil (Internal Mold) (Class Bivalvia (Indeterminate genus)) — fossil
fossil

Bivalve Fossil (Internal Mold)

Class Bivalvia (Indeterminate genus)

AI-generated identification · may be incorrect

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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Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

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Fossiliferous limestone (likely a crinoidal or shell-fragment limestone)

Bioclastic limestone, composed chiefly of calcite (CaCO₃)

sedimentary
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Calcite-rich limestone (primarily CaCO₃); exact identification is uncertain from the image

sedimentary
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Weathered fossil bone fragment (identification uncertain)

Fossilized bone; exact taxon and mineral composition cannot be determined from the image

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