fossil

Ammonite fossil

Fossilized ammonoid cephalopod; likely an indeterminate Jurassic–Cretaceous ammonite

AI-generated identification · may be incorrect

Mineralized shell showing strong radial ribs and involute spiral coiling; commonly calcite replacing aragonite, with hardness about 3–4, earthy to dull luster, and gray-brown coloration. The surrounding matrix appears calcareous and weathered.

Identified August 26, 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); this specimen is likely Mesozoic. Burial in marine sediment followed by compaction and mineral replacement preserved the shell.

Uses & applications

Primarily used for education, display, lapidary work, and fossil collecting; polished ammonites can be decorative. Commercial value depends on size, completeness, locality, preservation, and legal provenance.

Geological facts

The spiral partitions visible inside the shell are sutures, which strengthened the shell against water pressure. Ammonites are extinct relatives of modern squid, cuttlefish, and nautiluses.

Field identification & locations

Identify by the planispiral chambered shell, radiating ribs, and repeating suture pattern; test matrix cautiously because acid can damage calcite fossils. Common sources include Morocco, Madagascar, England, Germany, and North America.