sedimentary
Orthoceras Fossil Limestone
Orthoceras sp. (Calcium Carbonate, CaCO3)
AI-generated identification · may be incorrectHardness: 3-4 (Mohs scale), Color: Black to dark grey matrix with white or cream fossils, Luster: Vitreous when polished, Structure: Fine-grained limestone containing orthocone fossils.
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Physical properties
Hardness: 3-4 (Mohs scale), Color: Black to dark grey matrix with white or cream fossils, Luster: Vitreous when polished, Structure: Fine-grained limestone containing orthocone fossils.
Formation & geological history
Formed through the accumulation of organic remains on the ocean floor during the Paleozoic era, specifically the Ordovician period (approx. 400-500 million years ago). The shell segments were replaced by calcite or silica.
Uses & applications
Primarily used for decorative purposes, including tabletops, tiles, jewelry (pendants/cabochons), and as educational fossils for collectors.
Geological facts
Orthoceras were ancient cephalopods related to the modern squid and nautilus; they could grow from a few centimeters to over 14 feet long. Their name means 'straight horn'.
Field identification & locations
Identified by the distinct white, cone-shaped internal chambers (septa) against a dark matrix. Most commercial specimens are sourced from the Atlas Mountains in Morocco.
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