RocksdayCrinoid vs Fusulinid
To tell Crinoid from Fusulinid: Crinoid bits are round discs or plates, not spindles.
Fossil sea lilies — animals related to starfish — usually found as stacked, button-shaped stem pieces.
Photo: James St. John, CC BY 2.0
Wheat- or rice-shaped shells of late Paleozoic foraminifera. A limestone can be made of almost nothing else.
Photo: Wilson44691, CC BY-SA 3.0
Key differences
- Crinoid bits are round discs or plates, not spindles.
Side by side
| Property | Crinoid | Fusulinid |
|---|---|---|
| Type | Fossil | Fossil |
| Mohs hardness | 3 | 3–4 |
| Luster | Dull | Dull |
| Colors | Gray, White, Brown | Gray, White, Brown |
| Crystal system / structure | Calcite stem discs | Rice-grain foraminifera in limestone |
| Specific gravity | 2.6–2.8 | 2.6–2.7 |
| Found in | Burlington Limestone, Iowa; Indiana | Kansas; Texas |
Properties that are the same for both are grayed out.
How to identify crinoid
- Small round discs, often with a hole in the center.
- Stacked into stem segments like beads.
- Fizzes in acid (calcite).
Structure: Calcite stem discs
Full Crinoid guide →How to identify fusulinid
- Tiny grains the size of rice or wheat in limestone.
- A broken grain shows coiled chambers.
- The rock fizzes in acid.
Structure: Rice-grain foraminifera in limestone
Full Fusulinid guide →More comparisons
Frequently asked questions
What is the difference between crinoid and fusulinid?
Crinoid is a fossil with a Mohs hardness of about 3 and a dull luster, usually gray, white or brown. Fusulinid is a fossil with a Mohs hardness of about 3–4 and a dull luster, usually gray, white or brown.
How can you tell crinoid from fusulinid?
Crinoid bits are round discs or plates, not spindles.
Could you tell them apart from a blurry close-up?
Play today's Rocksday