sedimentary

Orthoceras fossil in limestone

Orthoceras (extinct genus of cephalopod)

AI-generated identification · may be incorrect

Hardness: 3-4 (calcite matrix); Color: Black or dark grey matrix with white or cream-colored fossil; Luster: Polished earthy; Crystal Structure: Microcrystalline with visible internal chambers (septa).

Hardness: 3-4 (calcite matrix)
Color: Black or dark grey matrix with white or cream-colored fossil
Luster: Polished earthy

Identified June 2, 2026More sedimentary →

Explore Orthoceras fossil in limestone in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed during the Ordovician period (approx. 488 - 443 million years ago) in marine environments when shells settled on the sea floor and were buried by sediment.

Uses & applications

Primarily used as decorative display pieces, paperweights, jewelry (pendants), and internal architectural tiling.

Geological facts

Orthoceras name means 'straight horn'. They are ancestors to the modern squid and lived inside their shells. They could grow from a few inches to over 14 feet long.

Field identification & locations

Identify by the distinctive bullet or cone-shaped shell with internal chamber divisions (septa) and a central tube (siphuncle). Mostly found in the Anti-Atlas Mountains of Morocco.