Rock Identifier
Ammonite fossil (Ammonoidea (coiled cephalopod fossil; exact genus indeterminate)) — fossil
fossil

Ammonite fossil

Ammonoidea (coiled cephalopod fossil; exact genus indeterminate)

AI-generated identification · may be incorrect

Small, planispirally coiled fossil with strong ribbing and a visible suture-like pattern; likely calcite-replaced shell in a tan-brown matrix. Original shell mineral was aragonite; preserved material is commonly calcite, hardness about 3–4, dull to satin luster, with radial symmetry and chambered coiling.

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Physical properties

Small, planispirally coiled fossil with strong ribbing and a visible suture-like pattern; likely calcite-replaced shell in a tan-brown matrix. Original shell mineral was aragonite; preserved material is commonly calcite, hardness about 3–4, dull to satin luster, with radial symmetry and chambered coiling.

Formation & geological history

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

Uses & applications

Primarily a teaching, collecting, and decorative specimen; polished ammonites and high-quality examples may be sold as fossils or jewelry components.

Geological facts

The spiral chambers housed a buoyant animal related to modern nautiluses, squids, and octopuses. The coiled form and sutures are diagnostic of ammonites, though this specimen may also be a small gastropod or partial internal mold.

Field identification & locations

Identify by its tightly coiled planispiral shape, repeated chambers, and ribbed or sutured surface; common sources include Morocco, Madagascar, the United Kingdom, Canada, and the United States. A clear photograph cannot confirm species-level identification.

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