sedimentary
Ammonite Fossil
Ammonoidea (subclass)
Spiral shape, internal chambers (septa), hardness of 3.5-4 (Mohs), tan to earthy brown color, waxy to vitreous luster inside chambers, calcified structure.
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Physical properties
Spiral shape, internal chambers (septa), hardness of 3.5-4 (Mohs), tan to earthy brown color, waxy to vitreous luster inside chambers, calcified structure.
Formation & geological history
Formed through permineralization of the shells of extinct marine cephalopods during the Devonian through the Cretaceous periods (approx. 400 to 66 million years ago).
Uses & applications
Educational purposes, museum displays, jewelry (when iridescent or polished), and decorative fossil collecting.
Geological facts
Ammonites are more closely related to octopuses and squids than to the modern Nautilus they resemble. Their shells grew by adding new, larger chambers as the animal grew.
Field identification & locations
Look for the distinct spiral shape and 'suture' patterns on the surface. Commonly found in sedimentary basins like the Jurassic Coast in the UK or Morocco.
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