RocksdayCrinoid vs Nummulite
To tell Crinoid from Nummulite: Crinoid stem pieces are small discs, often with a center hole, not a spiral coin.
Fossil sea lilies — animals related to starfish — usually found as stacked, button-shaped stem pieces.
Photo: James St. John, CC BY 2.0
Coin-shaped shells of giant foraminifera, common in Eocene and Miocene limestones around the Mediterranean.
Photo: Wilson44691, Public domain
Key differences
- Crinoid stem pieces are small discs, often with a center hole, not a spiral coin.
Side by side
| Property | Crinoid | Nummulite |
|---|---|---|
| Type | Fossil | Fossil |
| Mohs hardness | 3 | 3 |
| Luster | Dull | Dull |
| Colors | Gray, White, Brown | White, Gray, Yellow |
| Crystal system / structure | Calcite stem discs | Coin-shaped foraminifera |
| Specific gravity | 2.6–2.8 | 2.6–2.7 |
| Found in | Burlington Limestone, Iowa; Indiana | Egypt; Mediterranean region |
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 nummulite
- Flat disks from about a centimeter to a few centimeters across.
- A broken one shows a tight spiral of tiny chambers.
- The limestone fizzes in acid.
Structure: Coin-shaped foraminifera
Full Nummulite guide →More comparisons
Frequently asked questions
What is the difference between crinoid and nummulite?
Crinoid is a fossil with a Mohs hardness of about 3 and a dull luster, usually gray, white or brown. Nummulite is a fossil with a Mohs hardness of about 3 and a dull luster, usually white, gray or yellow.
How can you tell crinoid from nummulite?
Crinoid stem pieces are small discs, often with a center hole, not a spiral coin.
Could you tell them apart from a blurry close-up?
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