fossil

Polished ammonite fossil

Ammonoidea (fossil cephalopod), likely a small planispiral ammonite in limestone/mudstone

AI-generated identification · may be incorrect

Gray-black, highly polished, with a visible coiled chamber pattern and reflective carbonate surface; fossil shell is commonly calcite-replaced or preserved in limestone. Calcite hardness is about Mohs 3, with vitreous to waxy luster; specific gravity roughly 2.6–2.8.

Identified September 15, 2026More fossil →

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Physical properties

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 fine marine sediment and later mineralized during diagenesis; the specimen has been cut and polished.

Uses & applications

Primarily a collectible, educational specimen, or decorative stone; polished ammonites are sometimes used in jewelry and small display objects.

Geological facts

The coiled divisions are septa/chambers, while the outer edge may show the suture pattern characteristic of ammonites. Exact species and age require locality and close examination.

Field identification & locations

Identify by the tightly coiled, chambered spiral and fossil texture rather than random veining; common sources include Madagascar, Morocco, Canada, and Europe. Approximate value: $10–$60 for a small polished specimen, higher for large, complete, or exceptionally patterned examples.