Rock Identifier
Ammonite Fossil (Ammonoidea) — fossil
fossil

Ammonite Fossil

Ammonoidea

AI-generated identification · may be incorrect

Hardness varies around 4 on the Mohs scale depending on mineralization, featuring a distinct planispiral shell with complex ribbing and sutures. Color ranges from grey and brown to iridescent if pyritized or nacreous.

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Physical properties

Hardness varies around 4 on the Mohs scale depending on mineralization, featuring a distinct planispiral shell with complex ribbing and sutures. Color ranges from grey and brown to iridescent if pyritized or nacreous.

Formation & geological history

Formed from marine cephalopod shells buried in sedimentary marine deposits during the Mesozoic era, approximately 66 to 240 million years ago.

Uses & applications

Widely collected, used in educational displays, cut for decorative jewelry, and utilized as an index fossil for relative dating.

Geological facts

Ammonites are closely related to modern octopuses and squids rather than nautiluses. They went extinct at the end of the Cretaceous period alongside the non-avian dinosaurs.

Field identification & locations

Found worldwide in marine sedimentary rock layers, particularly in clay, limestone, and shale formations. Easily identified by their characteristic coiled shell morphology and suture patterns.

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Phylum Echinodermata, Class Crinoidea

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Fossiliferous limestone (likely a crinoidal or shell-fragment limestone) (Bioclastic limestone, composed chiefly of calcite (CaCO₃)) — sedimentary

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Bioclastic limestone, composed chiefly of calcite (CaCO₃)

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Calcite-rich limestone (primarily CaCO₃); exact identification is uncertain from the image

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Weathered fossil bone fragment (identification uncertain)

Fossilized bone; exact taxon and mineral composition cannot be determined from the image

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