fossil
Bivalve Fossil (Clam Fossil)
Class Bivalvia (likely Gryphaea or similar Order)
Hardness: 3-4 (calcite Replacement), Color: Grey, black, tan, Luster: Dull to earthy, Structure: Ribbed shell impressions (costae), specific gravity: 2.7
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Physical properties
Hardness: 3-4 (calcite Replacement), Color: Grey, black, tan, Luster: Dull to earthy, Structure: Ribbed shell impressions (costae), specific gravity: 2.7
Formation & geological history
Formed in marine sedimentary environments where shells were buried by sediment, eventually mineralized via permineralization or replacement. Likely Mesozoic or Cenozoic in age.
Uses & applications
Scientific study, educational tools, and personal fossil collections.
Geological facts
Bivalves are one of the most successful groups of mollusks. The famous 'Devil's Toenail' is a specific type of curved bivalve fossil similar to the curved specimen in the image.
Field identification & locations
Identify by looking for symmetrical 'ribs' or lines of growth and a distinct hinge area. Found in limestone or shale outcrops throughout central Mexico (Quer taro/Hidalgo region).
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