fossil

Fossilized Oyster Shell

Gryphaea or Exogyra (Family Ostreidae)

Hardness: 3-4 (calcite/aragonite), Color: Gray, brown, or off-white, Luster: Dull to pearly, Structure: Lamellar or foliated calcite layers, Specific Gravity: 2.6-2.8

Identified August 2, 2026More fossil →

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Physical properties

Hardness: 3-4 (calcite/aragonite), Color: Gray, brown, or off-white, Luster: Dull to pearly, Structure: Lamellar or foliated calcite layers, Specific Gravity: 2.6-2.8

Formation & geological history

Formed in marine environments during the Mesozoic and Cenozoic eras, typically through the replacement or preservation of calcium carbonate shells in sedimentary rock layers like limestone, marl, or shale.

Uses & applications

Used primarily as educational specimens, in fossil collecting, paleoecological research, and sometimes in lapidary work or decorative displays.

Geological facts

Colloquially known as 'devil's toenails', these fossilized oyster shells are common index fossils that help geologists date sedimentary strata.

Field identification & locations

Found worldwide in shallow marine sedimentary deposits, road cuts, and creek beds. Identified by their curved, cupped shape and distinct concentric growth rings.

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