fossil

Ammonite Fossil

Ammonoidea

Hardness around 3.5 to 4 on Mohs scale (typically replaced by calcite, aragonite, or pyrite); light brown to tan color; dull to earthy luster; planar spiral coiled shell structure with visible sutured chambers.

Identified July 26, 2026More fossil →

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Physical properties

Formation & geological history

Formed through permineralization or replacement of ancient marine mollusk shells that lived during the Devonian to Cretaceous periods (approx. 400 to 66 million years ago). Typically found in marine sedimentary rock layers like limestone and shale.

Uses & applications

Used primarily as educational specimens, decorative display pieces, jewelry (cabochons and pendants), and highly valued by fossil collectors.

Geological facts

Ammonites were shelled cephalopods related to modern squids, octopuses, and cuttlefish. Their complex suture lines on the inner shell walls are crucial for scientific classification and biostratigraphy.

Field identification & locations

Identified by its distinctive coiled, chambered planispiral shell pattern with visible ribbing or suture lines. Commonly found in Mesozoic marine sedimentary formations worldwide, such as the Jurassic Coast in the UK and Madagascar.