fossil

Polished fossil shell, likely orthocone nautiloid

Orthoceras-type fossil; fossilized cephalopod shell, commonly marketed as Orthoceras

AI-generated identification · may be incorrect

Cream to gray calcitic shell with brown iron-oxide staining and dark matrix; polished surface is dull to waxy. Calcite hardness 3, Mohs; rhombohedral crystal structure, with shell chambers or growth layers often visible.

Identified August 12, 2026More fossil →

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Physical properties

Formation & geological history

A marine cephalopod shell, probably from Paleozoic carbonate sediments, commonly Devonian–Permian (about 419–252 million years old), later mineralized by calcite and iron oxides. The elongated form may also represent a straight-shelled nautiloid or a polished fossil fragment rather than true Orthoceras.

Uses & applications

Used mainly as a decorative and collectible fossil, including bookends, ornaments, and jewelry components; not generally used in construction. Value depends on authenticity, preservation, size, and polish.

Geological facts

“Orthoceras” is widely used commercially for several straight-shelled nautiloid fossils, not necessarily the genus Orthoceras. Chambered internal structure is the key diagnostic feature.

Field identification & locations

Look for repeated transverse chambers, septa, and sometimes a central siphuncle; calcite reacts weakly with dilute hydrochloric acid. Common commercial specimens come from Morocco and Madagascar; typical value is $10–$60, with exceptional examples $100–$300.