sedimentary

Orthoceras Fossil in Limestone

Orthoceras regulare (Class Cephalopoda; Order Orthocerida)

AI-generated identification · may be incorrect

Hardness: 3-4 (Calcite matrix). Color: Black to dark brown matrix with white or grey fossil. Luster: Vitreous to dull. Structure: Long, straight conical shells with internal septa (chambers).

Hardness: 3-4 (Calcite matrix)
Color: Black to dark brown matrix with white or grey fossil
Luster: Vitreous to dull

Identified April 2, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (Calcite matrix). Color: Black to dark brown matrix with white or grey fossil. Luster: Vitreous to dull. Structure: Long, straight conical shells with internal septa (chambers).

Formation & geological history

Formed through the accumulation of marine sediments during the Paleozoic era (specifically Middle Ordovician, approx. 400-450 million years ago). The animal's shell was buried in mud, which slowly lithified into limestone as minerals filled the hollow chambers.

Uses & applications

Used primarily for decorative purposes, collector specimens, jewelry (cabochons), and educational displays.

Geological facts

Orthoceras were ancestors to the modern squid and lived in a straight, conical shell. The name means 'straight horn'. Most polished specimens like this one come from large fossil beds in the Atlas Mountains of Morocco.

Field identification & locations

Identify by looking for a straight, bullet-shaped conical structure with distinct horizontal lines (septa) or a central tube (siphuncle). Commonly found in marine limestone deposits globally, particularly in Northern Africa and parts of Europe.