sedimentary
Fossilized Pycnodonte Oyster
Pycnodonte (Gryphaeostrea) species; Composition is Calcium Carbonate (Calcite/Aragonite)
Hardness: 3 (Calcite); Color: Tan, cream, or silvery-grey; Luster: Dull to pearly (nacreous); Structure: Asymmetrical bivalve shell with a concave shape; Specific Gravity: Approx 2.7
- Hardness
- 3 (Calcite)
- Color
- Tan, cream, or silvery-grey
- Luster
- Dull to pearly (nacreous)
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Physical properties
Hardness: 3 (Calcite); Color: Tan, cream, or silvery-grey; Luster: Dull to pearly (nacreous); Structure: Asymmetrical bivalve shell with a concave shape; Specific Gravity: Approx 2.7
Formation & geological history
Formed through the process of permineralization or replacement of organic shell matter in shallow marine environments. These specimens typically date back to the Cretaceous period (approx. 66-145 million years ago).
Uses & applications
Primary use is for educational purposes, paleontological study, and as decorative collector's items. Fossiliferous limestone is also sometimes used in construction.
Geological facts
Members of the Pycnodonte genus are often called 'foam oysters' because their shells contain bubble-like cavities that helped them stay stable on soft, muddy sea floors.
Field identification & locations
Identify by looking for the distinct 'comma' or 'cup' shape of the shell and the presence of nacreous (pearly) layers. Commonly found in Mesozoic-era marine sedimentary outcrops such as those in Texas, New Jersey, and Europe.
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