Fossilized Oyster Shell

Physical Properties

Hardness: 3 (Mohs scale), Color: Brown, gray, tan, Luster: Dull to pearly inside, Crystal Structure: Trigonal (as calcite or aragonite), Cleavage: Perfect, Specific Gravity: 2.7

Formation & Geological History

Formed through the process of permineralization or replacement where an ancient oyster's calcium carbonate shell is buried in sediment and chemically altered over millions of years, often in marine environments from the Mesozoic to Cenozoic eras.

Uses & Applications

Used primarily as educational specimens, biological research, collector items, and occasionally crushed for high-calcium fertilizer or industrial lime if found in massive quantities.

Geological Facts

Commonly known as 'Devil's Toenails' (specifically for the genus Gryphaea), these fossils indicate that the region where they were found was once under a shallow sea. Some fossils contain druzy quartz or calcite crystals that grew inside the cavity after death.

Field Identification & Locations

Identify by visible growth lines (lamellae), calcified texture, and the distinctive 'hinge' area of the bivalve. Found in sedimentary deposits like limestone or shale cliffs and riverbeds.

Identified on: 4/20/2026

Mode: Standard