fossil

Orthoceras Fossil

Orthoceras regulare

Hardness: 3-4 (Mohs scale), Color: Black to dark grey matrix with white or cream fossils, Luster: Polished/Waxy, Crystal Structure: Calcified shell chambers, Specific Gravity: 2.7

Identified July 18, 2026More fossil →

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Physical properties

Hardness: 3-4 (Mohs scale), Color: Black to dark grey matrix with white or cream fossils, Luster: Polished/Waxy, Crystal Structure: Calcified shell chambers, Specific Gravity: 2.7

Formation & geological history

Formed in marine environments during the Ordovician period approximately 400-450 million years ago. These straight-shelled nautiloids were preserved in limestone or black shale as sediment solidified into rock.

Uses & applications

Primarily used for decorative purposes, jewelry (pendants and cabochons), educational displays, and as a popular collector item for fossil enthusiasts.

Geological facts

Orthoceras means 'straight horn'. These creatures were ancestors to the modern-day squid and octopus, reaching lengths from a few inches to over 14 feet. These specific black limestone specimens are almost exclusively sourced from the Atlas Mountains in Morocco.

Field identification & locations

Identified by the distinct straight, segmented conical shell and central siphuncle. Commonly found in large slabs in Morocco. Collectors should look for clear definition of the septa (the dividing walls between chambers).