fossil

Fossilized bivalve shell

Paleozoic–Mesozoic bivalve fossil; commonly classified as Bivalvia indet.

AI-generated identification · may be incorrect

Dark gray-brown, glossy to submetallic-looking shell with radial growth ribs and layered surface; original shell is chiefly calcium carbonate (aragonite or calcite), Mohs hardness about 3–4, with prominent hinge/valve curvature and no true crystal cleavage.

Identified August 25, 2026More fossil →

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Physical properties

Formation & geological history

A marine clam or related bivalve was buried in sediment, then mineralized or preserved as a compression/impression fossil during diagenesis; exact age and formation require locality and matrix analysis.

Uses & applications

Primarily a teaching, display, and collecting specimen; polished or stabilized examples may be sold decoratively, but it has no significant industrial use.

Geological facts

The visible ridges are growth lines or ribs, recording shell expansion; dark coloration commonly results from organic residues, iron/manganese minerals, or replacement during burial.

Field identification & locations

Identify it by paired-valve shape, hinge area, concentric growth lines, and sedimentary matrix; common in marine limestone and shale worldwide. A conclusive identification needs the opposite valve, hinge details, and locality.