Rock Identifier
Fossil bivalve shell (Ribbed pectinid or related bivalve; originally calcite/aragonite (CaCO₃), likely partially mineralized) — fossil
fossil

Fossil bivalve shell

Ribbed pectinid or related bivalve; originally calcite/aragonite (CaCO₃), likely partially mineralized

AI-generated identification · may be incorrect

Fan-shaped shell with strong radial ribs, concentric growth lines, and bilateral symmetry; gray-beige, dull to slightly pearly luster. Mohs hardness about 3–4 for calcitic shell; cleavage is not usually apparent, and specific gravity is roughly 2.6–2.9.

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Physical properties

Fan-shaped shell with strong radial ribs, concentric growth lines, and bilateral symmetry; gray-beige, dull to slightly pearly luster. Mohs hardness about 3–4 for calcitic shell; cleavage is not usually apparent, and specific gravity is roughly 2.6–2.9.

Formation & geological history

A marine bivalve shell preserved by burial and fossilization, commonly through recrystallization or replacement by calcite. Exact geologic age cannot be determined from the photograph and may range from Cenozoic to older.

Uses & applications

Primarily a collectible, educational specimen, or decorative object; fossil shell material is not generally used industrially or as gemstone material.

Geological facts

The radial ribs strengthened the shell against waves and predators. The visible growth lines record episodic growth, while the fan-like form is characteristic of scallops and related pectinids.

Field identification & locations

Identify it by its symmetrical fan shape, radiating ribs, and growth lines; distinguish it from a modern shell by mineralized weight, muted color, and lack of organic gloss. Common in marine sedimentary rocks and coastal fossil beds worldwide.

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