sedimentary
Orthoceras fossil in limestone
Orthoceras (extinct genus of cephalopod)
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
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Physical properties
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).
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.
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