sedimentary
Fossil Shell (Bivalve)
Phylum Mollusca, Class Bivalvia (typically composed of Calcium Carbonate / CaCO3)
Hardness: 3 (Mohs scale), Color: Cream, white, or tan (often with iron staining), Luster: Dull to pearly, Structure: Bilateral symmetry with concentric growth rings, Cleavage: None (conchoidal fracture).
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Physical properties
Hardness: 3 (Mohs scale), Color: Cream, white, or tan (often with iron staining), Luster: Dull to pearly, Structure: Bilateral symmetry with concentric growth rings, Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the process of permineralization or recrystallization of organic shell material within sedimentary layers. These specimens typically form in marine or freshwater environments during various geological periods, often the Cenozoic or Mesozoic eras.
Uses & applications
Used primarily for educational purposes, scientific research (paleontology), and by amateur collectors. Some limestone containing high fossil density is used as decorative building stone.
Geological facts
Bivalves have existed for over 500 million years. Unlike modern shells, fossilized versions have often had their original aragonite replaced by more stable calcite or silica over millions of years.
Field identification & locations
Identify in the field by looking for distinct concentric 'growth lines' and a hinge area (umbo). Commonly found in limestone outcrops, riverbeds, and coastal sedimentary cliffs.
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