fossil

Ammonite fossil

Fossilized ammonoid cephalopod; likely an involute ammonite, exact genus/species indeterminate

AI-generated identification · may be incorrect

A sedimentary fossil consisting mainly of calcite replacing the original aragonite shell and surrounding limestone/mudstone. Typically Mohs 3–4, cream to tan, dull to waxy luster, with a chambered planispiral shell and visible suture patterns; density is commonly about 2.6–2.8.

Identified August 30, 2026More fossil →

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Physical properties

Formation & geological history

Ammonites lived in marine environments during the Mesozoic Era, roughly 400–66 million years ago; the specimen most likely dates from the Jurassic or Cretaceous. Burial in marine sediment and later mineral replacement preserved the shell.

Uses & applications

Used as a geological teaching specimen, decorative object, and fossil collectible; polished ammonites are also used in jewelry and ornamental carvings.

Geological facts

The spiral chambers housed a squid-like animal, while the living chamber formed the outermost portion. The intricate lines are sutures between internal chambers, useful for classification and species identification.

Field identification & locations

Identify it by the coiled, segmented shell and radiating or branching sutures; it is commonly found in marine sedimentary rocks worldwide, especially Europe, North Africa, Madagascar, India, and western North America. Avoid acids and harsh cleaning, which can damage calcite.