Rock Identifier
Fossilized ammonite (Ammonoidea (likely an ammonite; exact genus indeterminate)) — fossil
fossil

Fossilized ammonite

Ammonoidea (likely an ammonite; exact genus indeterminate)

AI-generated identification · may be incorrect

A coiled, chambered fossil shell with gray-brown calcitic or aragonitic replacement, cream mineral infilling, weathered ridges, and subdued earthy luster. Original shell material is commonly converted to calcite; hardness about 3–4, with possible cleavage in calcite-rich areas.

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Physical properties

A coiled, chambered fossil shell with gray-brown calcitic or aragonitic replacement, cream mineral infilling, weathered ridges, and subdued earthy luster. Original shell material is commonly converted to calcite; hardness about 3–4, with possible cleavage in calcite-rich areas.

Formation & geological history

Ammonites were marine cephalopods that lived from the Devonian to the end-Cretaceous, becoming extinct about 66 million years ago. Their shells were buried in marine sediment and permineralized or replaced during diagenesis.

Uses & applications

Primarily a collectible, educational specimen, and decorative object; polished ammonites are sometimes used in jewelry and ornamental carvings.

Geological facts

The visible spiral growth pattern and repeated chamber divisions are diagnostic, although this specimen is heavily weathered and may be a partial or eroded ammonite.

Field identification & locations

Commonly found in Jurassic and Cretaceous marine rocks in Morocco, Madagascar, England, Germany, Canada, and the western United States. Confirm by exposing a cross-section or checking for regular internal septa and a continuous spiral; matrix removal can reduce authenticity and value.

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