sedimentary

Orthoceras Fossil in Limestone

Orthoceras (extinct genus of cephalopods) in Carboniferous or Devonian Limestone

Hardness: 3-4 (calcite matrix); Color: black or dark grey matrix with white or cream-colored fossils; Luster: matte to polished; Structure: straight, conical fossil nautiloid with internal septa; Specific gravity: ~2.7

Hardness: 3-4 (calcite matrix)
Luster: matte to polished

Identified February 21, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in marine environments as fossilized remains of predatory mollusks that lived approximately 360 to 450 million years ago. Found in marine sedimentary layers where minerals replaced organic matter over millions of years.

Uses & applications

Commonly used for home decor, jewelry, fossil collecting, educational specimens, and small ornamental carvings. Larger slabs are used for architectural panels.

Geological facts

Orthoceras means 'straight horn'. These creatures were prehistoric ancestors of the modern squid and octopus. The visible white lines in the fossil represent the internal chambers or 'septa' of its shell.

Field identification & locations

Identified by the distinct white, conical, or bullet-shaped patterns against a dark matrix. Frequently found in the Atlas Mountains of Morocco. Collectors should look for clear, well-preserved internal septal divisions.

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