RocksdayBaculites vs Orthoceras
The quickest way to tell Baculites from Orthoceras: Orthoceras fizzes; Baculites doesn't.
A straight-shelled ammonite from the Cretaceous. The shell is a long cone with complex, wavy suture lines.
Photo: DanielCD, 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
Quick tests
- Acid (vinegar or dilute HCl): Orthoceras fizzes; Baculites doesn't.
Key differences
- Orthoceras is a nautiloid with simple chamber walls, not frilled sutures.
Side by side
| Property | Baculites | Orthoceras |
|---|---|---|
| Type | Fossil | Fossil |
| Mohs hardness | 3–4 | 3–4 |
| Luster | Dull to pearly | Dull (polished in shops) |
| Colors | Gray, Brown, White, Gold | Black, Gray, Red |
| Crystal system / structure | Straight ammonite shell | Straight chambered shell (calcite) |
| Specific gravity | 2.6–2.8 | 2.6–2.8 |
| Found in | Pierre Shale, South Dakota; Montana | Erfoud, Morocco; Öland, Sweden |
Properties that are the same for both are grayed out.
How to identify baculites
- A straight section of shell, not a coil.
- Wavy, branching suture lines where the chambers met the shell.
- Often in shale. Shell material may fizz; a mold may not.
Structure: Straight ammonite shell
Full Baculites 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 baculites and orthoceras?
Baculites is a fossil with a Mohs hardness of about 3–4 and a dull to pearly luster, usually gray, brown, white or golden. 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 baculites from orthoceras?
Orthoceras fizzes; Baculites doesn't. Orthoceras is a nautiloid with simple chamber walls, not frilled sutures.
Could you tell them apart from a blurry close-up?
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