RocksdayCrinoid vs Horn Coral
To tell Crinoid from Horn Coral: Crinoid pieces are round stem discs, often with a hole.
Fossil sea lilies — animals related to starfish — usually found as stacked, button-shaped stem pieces.
Photo: James St. John, CC BY 2.0
A solitary rugose coral, shaped like a horn, with radial walls inside. The group died out at the end of the Permian.
Photo: James St. John, CC BY 2.0
Key differences
- Crinoid pieces are round stem discs, often with a hole.
Side by side
| Property | Crinoid | Horn Coral |
|---|---|---|
| Type | Fossil | Fossil |
| Mohs hardness | 3 | 3–4 |
| Luster | Dull | Dull |
| Colors | Gray, White, Brown | Gray, Brown, White |
| Crystal system / structure | Calcite stem discs | Calcite horn with septa |
| Specific gravity | 2.6–2.8 | 2.6–2.8 |
| Found in | Burlington Limestone, Iowa; Indiana | Falls of the Ohio; Midwest limestones |
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 horn coral
- Horn or cup shape, often in limestone.
- A cut end shows radial septa, like wheel spokes.
- Fizzes in acid.
Structure: Calcite horn with septa
Full Horn Coral guide →More comparisons
Frequently asked questions
What is the difference between crinoid and horn coral?
Crinoid is a fossil with a Mohs hardness of about 3 and a dull luster, usually gray, white or brown. Horn Coral is a fossil with a Mohs hardness of about 3–4 and a dull luster, usually gray, brown or white.
How can you tell crinoid from horn coral?
Crinoid pieces are round stem discs, often with a hole.
Could you tell them apart from a blurry close-up?
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