fossil

Fossilized bivalve shell fragment

Calcitic shell material, commonly Arca or related marine bivalve; primarily CaCO₃

AI-generated identification · may be incorrect

White to cream, strongly ribbed and weathered, with low vitreous-to-dull luster; calcite hardness is about 3 Mohs, with good cleavage in crystals but shell structure lacks obvious cleavage. The regular radial ribs and perforated-looking weathering are biological rather than crystalline textures.

Identified August 22, 2026More fossil →

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Physical properties

Formation & geological history

A marine mollusk shell accumulated in carbonate sediment and was buried, lithified, and variably replaced or preserved as calcite. Its precise geological age cannot be determined from the image; such shells range from modern subfossils to specimens millions of years old.

Uses & applications

Primarily a teaching, decorative, and collecting specimen; fossil shell material is not generally used structurally or as gemstone material.

Geological facts

The parallel ribs strengthened the shell against wave and predator damage. Dark spots may be sediment, mineral staining, or small dissolution pits rather than natural shell openings.

Field identification & locations

Identify it by bilateral shell curvature, repeated radial ribs, and carbonate composition; vinegar or dilute acid may fizz, though this damages the specimen. Fossiliferous marine limestones and coastal deposits commonly contain similar shells.