sedimentary
Orthoceras Fossil in Limestone
Orthoceras regulare
AI-generated identification · may be incorrectHardness: 3-4 (Mohs scale), Color: Black matrix with white/grey fossil, Luster: Polished/Dull, Crystal Structure: Microcrystalline calcite matrix, Cleavage: None (concretionary)
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Physical properties
Hardness: 3-4 (Mohs scale), Color: Black matrix with white/grey fossil, Luster: Polished/Dull, Crystal Structure: Microcrystalline calcite matrix, Cleavage: None (concretionary)
Formation & geological history
Formed during the Ordovician period (approx. 488-443 million years ago) when the shells of cephalopods settled on the sea floor and were covered by sediment, eventually turning into limestone.
Uses & applications
Primarily used for decorative purposes, jewelry (pendants/cabochons), paperweights, and educational fossil collecting.
Geological facts
Orthoceras were ancient mollusks related to the modern squid and nautilus; they had straight, cone-shaped shells and could grow from a few centimeters to over 10 feet long.
Field identification & locations
Identifiable by the distinct white conical chambers against a dark limestone background; most common specimens available today are sourced from the Atlas Mountains in Morocco.
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