fossil

Fossil ammonite

Ammonoidea; likely a chambered ammonite mold/cast

AI-generated identification · may be incorrect

Fossilized coiled shell with ribbing and raised chambers; tan-brown, earthy luster, and irregular fracture. Original shell mineralogy is obscured, but it is commonly replaced or infilled by calcite; calcite hardness is Mohs 3 and specific gravity about 2.7.

Identified September 13, 2026More fossil →

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Physical properties

Formation & geological history

Ammonites were extinct marine cephalopods that lived from the Devonian to the end-Cretaceous extinction (~409–66 million years ago). Their shells were buried in marine sediment and later mineralized, commonly during Jurassic or Cretaceous diagenesis.

Uses & applications

Primarily a collectible, educational, and decorative specimen; polished ammonites may be used in ornaments and jewelry. Commercial value depends strongly on preservation, size, locality, and preparation.

Geological facts

The visible spiral and repeated ribbing are characteristic of ammonites, though the specimen appears weathered and partly eroded. Chamber partitions (septa) may be visible on a freshly prepared cross-section.

Field identification & locations

Identify by the planispiral coil, segmented chambers, and ribs; test cautiously for calcite fizz with dilute hydrochloric acid on an inconspicuous spot. Common sources include Morocco, Madagascar, the United Kingdom, Germany, and Canada.