fossil

Ammonite Fossil

Ammonoidea subclass (calcium carbonate / silica replacement)

Hardness: 3.5 to 4 (if calcite), Color: Grey, white, or brown shades, Luster: Vitreous to dull, Crystal structure: Orthorhombic or trigonal (depending on mineral replacement such as calcite or aragonite)

Hardness: 3

Identified August 3, 2026More fossil →

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Physical properties

Formation & geological history

Formed through the fossilization of marine mollusk shells from the Devonian to Cretaceous periods, typically through permineralization or replacement in marine sedimentary rock layers.

Uses & applications

Popular among fossil collectors, used in decorative items, jewelry, and educational displays.

Geological facts

Ammonites are extinct marine cephalopods closely related to modern-day nautiluses and squids. They are excellent index fossils used by geologists to date rock strata.

Field identification & locations

Found worldwide in marine sedimentary deposits, particularly in limestone, shale, and clay formations. Identified by their characteristic coiled, spiral shell structure.

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Phylum Echinodermata, Class Crinoidea

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Sedimentary bedrock formation (variable composition)

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Chert with Fossil Brachiopod

Microcrystalline Quartz (SiO2) with Calcitic Brachiopod inclusion

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Fossilized Crinoid Stem in Limestone

Crinoidea (Class) in Calcium Carbonate (CaCO3) matrix

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Fossiliferous Limestone

Limestone with embedded fossil cross-section

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Fossiliferous Limestone with Crinoid stems

Limestone (CaCO3) containing Crinoidea fossils

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