fossil

Ammonite Fossil

Ammonoidea (subclass)

Spiral shell shape with internal chambers (septa), hardness of 3.5 to 4 on Mohs scale, colors ranging from earthy browns and tans to pearlescent or metallic hues, often calcified or pyritized.

Identified July 10, 2026More fossil →

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Physical properties

Spiral shell shape with internal chambers (septa), hardness of 3.5 to 4 on Mohs scale, colors ranging from earthy browns and tans to pearlescent or metallic hues, often calcified or pyritized.

Formation & geological history

Formed from the remains of extinct marine cephalopods during the Devonian through the Cretaceous periods (approx. 400 to 66 million years ago). The shell fills with minerals like calcite or aragonite in sedimentary marine environments.

Uses & applications

Commonly used as decorative specimens, in jewelry (especially iridescent 'Ammolite' varieties), and as important index fossils for dating rock layers.

Geological facts

Ammonites are more closely related to modern octopuses and squids than to the nautilus they resemble. They went extinct at the same time as the dinosaurs.

Field identification & locations

Identify by its distinct planar spiral shape and suture patterns on the shell surface. Frequently found in shale or limestone cliffs in locations like Madagascar, Morocco, and the UK Jurassic Coast.