RocksdayBelemnite vs Orthoceras
To tell Belemnite from Orthoceras: Orthoceras is a straight shell with chamber walls across it.
The bullet-shaped calcite counterweight of an extinct squid relative. The chambered shell behind it is rarely preserved.
Photo: Ghedoghedo, CC BY-SA 3.0
Straight, cone-shaped shells of ancient nautiloids, often polished in black limestone plates.
Photo: Parent Géry, CC BY-SA 3.0
Key differences
- Orthoceras is a straight shell with chamber walls across it.
Side by side
| Property | Belemnite | Orthoceras |
|---|---|---|
| Type | Fossil | Fossil |
| Mohs hardness | 3 | 3–4 |
| Luster | Vitreous to dull | Dull (polished in shops) |
| Colors | Brown, Gray, White | Black, Gray, Red |
| Crystal system / structure | Solid calcite guard | Straight chambered shell (calcite) |
| Specific gravity | 2.6–2.7 | 2.6–2.8 |
| Found in | Lyme Regis, England; Holzmaden, Germany | Erfoud, Morocco; Öland, Sweden |
Properties that are the same for both are grayed out.
How to identify belemnite
- A solid, finger-like or bullet-shaped stone.
- Broken ends may show radiating calcite.
- Fizzes in acid. No chambers running down the length.
Structure: Solid calcite guard
Full Belemnite guide →How to identify orthoceras
- Long straight cones with chamber walls across them.
- Often in polished black or red limestone.
- Fizzes in acid.
Structure: Straight chambered shell (calcite)
Full Orthoceras guide →More comparisons
Frequently asked questions
What is the difference between belemnite and orthoceras?
Belemnite is a fossil with a Mohs hardness of about 3 and a vitreous to dull luster, usually brown, gray or white. Orthoceras is a fossil with a Mohs hardness of about 3–4 and a dull luster, usually black, gray or red.
How can you tell belemnite from orthoceras?
Orthoceras is a straight shell with chamber walls across it.
Could you tell them apart from a blurry close-up?
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