fossil

Fossilized ammonite

Ammonoidea (likely a ribbed Jurassic–Cretaceous ammonite), replaced mainly by calcite or silica

AI-generated identification · may be incorrect

Coiled, chambered shell with strong ribs and a planispiral form; typically Mohs 3–7 depending on replacement mineral, with gray-brown color and dull to waxy luster. Original shell was aragonite, commonly recrystallized to calcite.

Identified August 8, 2026More fossil →

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Physical properties

Formation & geological history

Ammonites were marine cephalopods that lived from the Devonian to the end-Cretaceous extinction (~400–66 million years ago). Their shells were buried in marine sediment and fossilized through mineral replacement and infilling.

Uses & applications

Primarily a collector, educational, and decorative specimen; polished ammonites are used in jewelry and display. Value depends strongly on completeness, preservation, size, and provenance.

Geological facts

The visible spiral ribs are shell ornamentation, not growth rings of a mineral crystal. Ammonite fossils are especially abundant in Jurassic rocks of Madagascar, Morocco, the United Kingdom, Germany, and Alberta, Canada.

Field identification & locations

Identify by the involute spiral, repeated chambers, and radial ribs; a cross-section may reveal septa and suture patterns. This specimen appears fragmentary and heavily mineralized rather than gem-quality.