fossil

Ammonite fossil

Fossilized ammonoid cephalopod; likely an ammonite such as *Ammolytoceras* or a related Jurassic–Cretaceous genus

AI-generated identification · may be incorrect

Coiled, chambered shell with radial ribs, preserved mainly as calcite/aragonite replaced by calcite and dark matrix. Mohs hardness about 3–4; pearly to dull luster; commonly gray, cream, brown, or black; spiral symmetry and septa are diagnostic.

Identified September 22, 2026More fossil →

Explore Ammonite fossil in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Ammonites were marine cephalopods whose shells accumulated on ancient seafloors and fossilized through mineral replacement and compaction, typically during the Mesozoic Era (252–66 million years ago).

Uses & applications

Collected as fossils and used decoratively; polished ammonites and ammonite jewelry are popular, while rare iridescent specimens have gem value.

Geological facts

The visible spiral consists of successive chambers separated by internal walls; the animal occupied the outermost chamber. The dark material may be mineralized shell or sediment filling.

Field identification & locations

Identify by the planispiral coil, ribs, and chamber pattern; common sources include Morocco, Madagascar, Europe, and North America. Avoid acids and harsh cleaning, which can damage calcite-rich specimens.