fossil

Ammonite fossil

Ammonoidea (likely an involute ammonite; exact genus requires preparation and context)

AI-generated identification · may be incorrect

Fossilized, planispirally coiled shell with distinct chambers and a central suture pattern; usually calcite-replaced or preserved as a mineralized mold. Hardness commonly 3–4, gray-brown, earthy to dull luster; original aragonite is typically recrystallized to calcite.

Identified August 28, 2026More fossil →

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Physical properties

Formation & geological history

Ammonites were marine cephalopods that lived from the Devonian to the Cretaceous, becoming extinct at about 66 million years ago. The shell was buried in marine sediment and mineralized during diagenesis.

Uses & applications

Primarily a display, educational, and collecting specimen; polished ammonites are used in jewelry and décor. Value depends strongly on size, completeness, preservation, locality, and visible sutures.

Geological facts

The spiral is a shell, not a mineral crystal; internal chambers were connected by a siphuncle. The pictured specimen appears naturally weathered and may be a cross-section or exposed outer shell.

Field identification & locations

Common in marine sedimentary rocks worldwide, especially Jurassic and Cretaceous strata in Madagascar, Morocco, England, Germany, Canada, and the western United States. Identify by the coiled chambered shell and ammonitic sutures; vinegar fizz can indicate calcite, but avoid damaging it.