fossil

Fossil ammonite

Ammonoidea (likely a ribbed, involute ammonite; exact genus requires locality and preservation details)

AI-generated identification · may be incorrect

Fossilized coiled cephalopod shell, brown/tan, dull to earthy luster, with strong repetitive ribs; commonly calcite-replaced or preserved as a limestone/impression. Original shell calcite/aragonite; Mohs hardness typically about 3–4, specific gravity roughly 2.6–2.8.

Identified September 13, 2026More fossil →

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Physical properties

Formation & geological history

Ammonites were marine mollusks that lived from the Devonian to the end-Cretaceous, becoming extinct about 66 million years ago. Their shells accumulated in marine sediments and were buried, lithified, and mineralized during fossilization.

Uses & applications

Primarily a collector, educational, and decorative specimen; polished ammonites are used in jewelry and ornamental objects. Commercial value depends heavily on size, completeness, rib detail, locality, and preparation.

Geological facts

The visible ridges are shell ribs, not biological bones; the specimen appears to be a partial external mold or heavily mineralized shell. Ammonites are especially useful index fossils for dating Mesozoic marine rocks.

Field identification & locations

Identify by a planispiral coiled form, chambered structure, and regular ribs or sutures; compare the opposite side and look for a central coil. Common sources include Morocco, Madagascar, the United Kingdom, Germany, and Canada.