fossil

Fossiliferous limestone with ammonite fossil

Ammonite (subclass Ammonoidea) preserved in calcitic limestone, primarily CaCO₃

AI-generated identification · may be incorrect

Gray-white, fine-grained carbonate matrix with a raised spiral ammonite shell and chamber sutures; calcite has Mohs hardness 3, vitreous to dull luster, rhombohedral cleavage, and specific gravity about 2.7. The fossil itself may be replaced or infilled by calcite, pyrite, or iron-stained minerals.

Identified September 12, 2026More fossil →

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Physical properties

Formation & geological history

Ammonites were extinct marine cephalopods that lived from the Devonian to the end-Cretaceous, about 409–66 million years ago. Their shells accumulated on ancient seafloors and were buried, lithified, and fossilized in limestone.

Uses & applications

Used for education, paleontological study, décor, and collectible specimens; polished or cut ammonites are sometimes sold as jewelry or ornaments.

Geological facts

The visible spiral is divided into chambers once used for buoyancy control; complex sutures can help identify ammonite groups and geological age.

Field identification & locations

Identify by the coiled planispiral shell, repeated chambers, and radiating or branching sutures; common deposits occur in Jurassic and Cretaceous marine limestones worldwide, especially Morocco, Madagascar, England, and Germany.