RocksdayBaculites vs Belemnite
The quickest way to tell Baculites from Belemnite: Belemnite 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
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
Quick tests
- Acid (vinegar or dilute HCl): Belemnite fizzes; Baculites doesn't.
Key differences
- A belemnite guard is a solid calcite rod with no sutures.
- Baculites is a straight ammonite with wavy suture lines, not a solid rod.
Side by side
| Property | Baculites | Belemnite |
|---|---|---|
| Type | Fossil | Fossil |
| Mohs hardness | 3–4 | 3 |
| Luster | Dull to pearly | Vitreous to dull |
| Colors | Gray, Brown, White, Gold | Brown, Gray, White |
| Crystal system / structure | Straight ammonite shell | Solid calcite guard |
| Specific gravity | 2.6–2.8 | 2.6–2.7 |
| Found in | Pierre Shale, South Dakota; Montana | Lyme Regis, England; Holzmaden, Germany |
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 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 →More comparisons
Frequently asked questions
What is the difference between baculites and belemnite?
Baculites is a fossil with a Mohs hardness of about 3–4 and a dull to pearly luster, usually gray, brown, white or golden. Belemnite is a fossil with a Mohs hardness of about 3 and a vitreous to dull luster, usually brown, gray or white.
How can you tell baculites from belemnite?
Belemnite fizzes; Baculites doesn't. A belemnite guard is a solid calcite rod with no sutures. Baculites is a straight ammonite with wavy suture lines, not a solid rod.
Could you tell them apart from a blurry close-up?
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