fossil

Ammonite fossil

Fossilized ammonoid cephalopod; likely an ammonite such as Desmoceras or similar Jurassic–Cretaceous form

AI-generated identification · may be incorrect

A coiled, ribbed fossil mold/cast with a visible suture pattern, preserved mainly as calcite-replaced shell in a tan limestone/mudstone matrix. Original shell aragonite commonly recrystallizes to calcite; Mohs hardness about 3–4, dull to earthy luster, with chambered spiral structure.

Identified August 26, 2026More fossil →

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Physical properties

Formation & geological history

Ammonites lived in marine oceans and were buried in fine sediment after death; mineral-rich groundwater later lithified the sediment and replaced the shell. Most comparable specimens are Mesozoic, roughly 201–66 million years old.

Uses & applications

Primarily a display, educational, and collector specimen; polished ammonites are also used decoratively and occasionally in jewelry. It has little industrial value.

Geological facts

Ammonites were extinct marine cephalopods related to modern nautiluses, squid, and octopuses—not snails. Their chambered shells and rapidly evolving sutures make them important index fossils for dating marine rocks.

Field identification & locations

Identify it by the planispiral coil, repeated ribs, chamber divisions, and ammonitic sutures; common sources include Madagascar, Morocco, England, Germany, and Alberta. Estimated value: about $20–$100 for a common partial specimen of this size, or $100–$500+ if exceptionally complete, large, or well-prepared.