fossil

Ammonite fossil

Ammonoidea; likely a polished small ammonite, possibly Cleoniceras

AI-generated identification · may be incorrect

Fossilized, planispirally coiled shell with visible chamber septa and a dark gray-to-black mineralized matrix; polished surface has a subdued luster. Original shell was aragonite/calcite, with fossil hardness typically about 3–6 depending on replacement minerals.

Identified August 13, 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. The shell was buried in marine sediment and later mineralized, commonly by calcite, pyrite, or silica.

Uses & applications

Used primarily as a decorative fossil, educational specimen, and collector piece; polished ammonites are sometimes set in jewelry. Value depends heavily on species, size, preservation, polish, and provenance.

Geological facts

The spiral is a chambered shell, not a crystal-growth pattern; the animal occupied the outermost chamber. Septal sutures may be visible as intricate lines across the whorls.

Field identification & locations

Identify by the coiled, segmented shell and repeated chamber structure; common sources include Madagascar, Morocco, Canada, and England. Avoid acids and harsh abrasion, which can damage carbonate material and polish.