fossil

Ammonite fossil

Fossilized ammonoid cephalopod, commonly classified within Ammonoidea

AI-generated identification · may be incorrect

Typically calcite-replaced shell with a coiled, chambered form and radiating suture patterns; Mohs hardness about 3–4, dull to pearly luster, gray-beige color, and good cleavage in calcite. The visible specimen appears polished or naturally weathered and is likely a cross-section.

Identified August 22, 2026More fossil →

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Physical properties

Formation & geological history

Ammonoids were marine animals that lived from the Devonian to the end-Cretaceous (about 409–66 million years ago); their shells were buried in carbonate-rich sediment and mineralized during diagenesis. Exact age and species require locality and detailed suture analysis.

Uses & applications

Used as educational specimens, decorative objects, and fossils for collectors; high-quality iridescent ammonites are occasionally used in jewelry. Ordinary examples have modest commercial value.

Geological facts

The shell’s chambers were connected by a siphuncle and helped regulate buoyancy. The spiral shape is not a mineral crystal but the preserved architecture of the animal’s shell.

Field identification & locations

Identify by the planispiral coil, repeated chambers, and fine septal sutures; common deposits occur in Morocco, Madagascar, Canada, the United Kingdom, and Germany. Avoid acids, which can dissolve calcite-rich specimens.