Rock Identifier
Ammonite Fossil (Ammonoidea subclass (calcium carbonate / silica replacement)) — fossil
fossil

Ammonite Fossil

Ammonoidea subclass (calcium carbonate / silica replacement)

AI-generated identification · may be incorrect

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
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Physical properties

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)

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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Crinoid Stem Fossil in Matrix (Phylum Echinodermata, Class Crinoidea) — fossil

Crinoid Stem Fossil in Matrix

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

Fossiliferous limestone (likely a crinoidal or shell-fragment limestone)

Bioclastic limestone, composed chiefly of calcite (CaCO₃)

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Rounded sedimentary pebble

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Chert with Fossil Brachiopod

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