RocksdayEurypterid vs Graptolite
To tell Eurypterid from Graptolite: Graptolites are thin saw-blade films, not a broad segmented animal.
Extinct chelicerates — relatives of horseshoe crabs and arachnids — often called sea scorpions. Most finds are pieces of the shell in dark rock.
Photo: H. Zell, CC BY-SA 3.0
Saw-blade or twig-like carbon films on black shale, left by tiny colonial animals. They are classic index fossils.
Photo: Grezmagro, CC BY-SA 4.0
Key differences
- Graptolites are thin saw-blade films, not a broad segmented animal.
Side by side
| Property | Eurypterid | Graptolite |
|---|---|---|
| Type | Fossil | Fossil |
| Mohs hardness | 3 | 2–3 |
| Luster | Dull | Dull |
| Colors | Black, Brown, Gray | Black, Gray, White |
| Crystal system / structure | Arthropod exoskeleton in shale or dolostone | Carbon film on shale |
| Specific gravity | 2.6–2.8 | 2.4–2.7 |
| Found in | Bertie Group, New York; Kokomo, Indiana | Dob's Linn, Scotland; New York |
Properties that are the same for both are grayed out.
How to identify eurypterid
- A segmented body, paddle-like swimming leg or crescent head shield.
- Usually flattened in black shale or a dolostone slab.
- No three-lobed body like a trilobite.
Structure: Arthropod exoskeleton in shale or dolostone
Full Eurypterid guide →How to identify graptolite
- Dark marks like a hacksaw blade, a tuning fork or a twig on shale.
- The fossil is a film, not a raised shell.
- The host rock splits into thin slabs.
Structure: Carbon film on shale
Full Graptolite guide →More comparisons
Frequently asked questions
What is the difference between eurypterid and graptolite?
Eurypterid is a fossil with a Mohs hardness of about 3 and a dull luster, usually black, brown or gray. Graptolite is a fossil with a Mohs hardness of about 2–3 and a dull luster, usually black, gray or white.
How can you tell eurypterid from graptolite?
Graptolites are thin saw-blade films, not a broad segmented animal.
Could you tell them apart from a blurry close-up?
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