RocksdayAmmonite vs Baculites
The quickest way to tell Ammonite from Baculites: Ammonite fizzes; Baculites doesn't.
Coiled shells of extinct squid-like sea creatures that vanished with the dinosaurs.
Photo: Llez (H. Zell)., CC BY-SA 3.0
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
Quick tests
- Acid (vinegar or dilute HCl): Ammonite fizzes; Baculites doesn't.
Key differences
- Typical ammonites are coiled.
Side by side
| Property | Ammonite | Baculites |
|---|---|---|
| Type | Fossil | Fossil |
| Mohs hardness | 3–4 | 3–4 |
| Luster | Pearly to dull | Dull to pearly |
| Colors | Brown, Gray, Gold, White | Gray, Brown, White, Gold |
| Crystal system / structure | Coiled shell (aragonite, calcite or pyrite) | Straight ammonite shell |
| Specific gravity | 2.6–2.9 | 2.6–2.8 |
| Found in | Jurassic Coast, England; Mahajanga, Madagascar | Pierre Shale, South Dakota; Montana |
Properties that are the same for both are grayed out.
How to identify ammonite
- Flat spiral shell with ribs.
- Wavy, frilly suture lines where internal walls met the shell.
- Often split and polished to show chambers.
Structure: Coiled shell (aragonite, calcite or pyrite)
Full Ammonite guide →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 →More comparisons
Frequently asked questions
What is the difference between ammonite and baculites?
Ammonite is a fossil with a Mohs hardness of about 3–4 and a pearly to dull luster, usually brown, gray, golden or white. Baculites is a fossil with a Mohs hardness of about 3–4 and a dull to pearly luster, usually gray, brown, white or golden.
How can you tell ammonite from baculites?
Ammonite fizzes; Baculites doesn't. Typical ammonites are coiled.
Could you tell them apart from a blurry close-up?
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