Rock Identifier
Ammonite fossil (Ammonoidea; likely a Jurassic or Cretaceous ammonite) — fossil
fossil

Ammonite fossil

Ammonoidea; likely a Jurassic or Cretaceous ammonite

AI-generated identification · may be incorrect

A coiled, planispiral fossil with a visible central coil and ribbed surface; the original shell is probably replaced or coated by calcite/iron oxides. Typical ammonite shell material is aragonite originally, commonly preserved as calcite; Mohs hardness about 3–4, pearly to dull luster, and chambered internal structure.

Identified More fossil →
Explore Ammonite fossil in the encyclopedia →

Identify your own rocks.

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

App StoreGoogle Play

Physical properties

A coiled, planispiral fossil with a visible central coil and ribbed surface; the original shell is probably replaced or coated by calcite/iron oxides. Typical ammonite shell material is aragonite originally, commonly preserved as calcite; Mohs hardness about 3–4, pearly to dull luster, and chambered internal structure.

Formation & geological history

Ammonites were extinct marine cephalopods. Their shells accumulated in seafloor sediments and fossilized through mineral replacement or infilling, commonly during the Jurassic–Cretaceous (201–66 million years ago).

Uses & applications

Primarily a collectible, educational specimen, or decorative object; polished examples are sometimes used in jewelry and ornamentation.

Geological facts

The spiral records the animal’s growing shell, while internal septa divided it into buoyancy chambers. The apparent ring-like coil and shell texture strongly support ammonite rather than a modern rock.

Field identification & locations

Common in Jurassic and Cretaceous marine strata, including parts of northern France, England, Germany, Morocco, and Madagascar. Around 48.9°N, 2.5°E, a fossil ammonite is geologically plausible from regional Mesozoic sedimentary formations, though exact origin cannot be confirmed from the photograph.

More like this

Other fossil specimens

Probable fossil-bearing rock or mineral concretion (Unidentified carbonate-rich concretion with a possible fossil inclusion) — fossil

Probable fossil-bearing rock or mineral concretion

Unidentified carbonate-rich concretion with a possible fossil inclusion

fossil
Likely fossil oyster shell (Fossilized bivalve shell; exact species cannot be identified from the image) — fossil

Likely fossil oyster shell

Fossilized bivalve shell; exact species cannot be identified from the image

fossil
Crinoid Stem Fossil in Matrix (Phylum Echinodermata, Class Crinoidea) — fossil

Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

fossil
Fossiliferous limestone (likely a crinoidal or shell-fragment limestone) (Bioclastic limestone, composed chiefly of calcite (CaCO₃)) — sedimentary

Fossiliferous limestone (likely a crinoidal or shell-fragment limestone)

Bioclastic limestone, composed chiefly of calcite (CaCO₃)

sedimentary
Porous limestone pebble (Calcite-rich limestone (primarily CaCO₃); exact identification is uncertain from the image) — sedimentary

Porous limestone pebble

Calcite-rich limestone (primarily CaCO₃); exact identification is uncertain from the image

sedimentary
Weathered fossil bone fragment (identification uncertain) (Fossilized bone; exact taxon and mineral composition cannot be determined from the image) — fossil

Weathered fossil bone fragment (identification uncertain)

Fossilized bone; exact taxon and mineral composition cannot be determined from the image

fossil