RocksdayCoquina vs Limestone
How to tell them apart
A rock made almost entirely of broken shells loosely cemented together.
Photo: PaleoNeolitic, CC BY 4.0
A rock made mostly of calcite, often from shells and skeletons of sea creatures. It dissolves to create caves.
Photo: Mike Davis, CC0
Key differences
- Limestone is denser and shells are less obvious.
Side by side
| Property | Coquina | Limestone |
|---|---|---|
| Type | Sedimentary rock | Sedimentary rock |
| Mohs hardness | 2.5–3.5 | 3–4 |
| Luster | Dull | Dull |
| Colors | White, Yellow, Brown | White, Gray, Brown |
| Crystal system / structure | Loosely cemented shell fragments | Varied, often fossiliferous |
| Specific gravity | 1.8–2.4 | 2.5–2.7 |
| Found in | St. Augustine, Florida; Shark Bay, Australia | Bedford, Indiana; Tura, Egypt |
Properties that are the same for both are grayed out.
How to identify coquina
- Visible shell pieces throughout.
- Porous and light.
- Fizzes strongly in acid.
Structure: Loosely cemented shell fragments
Full Coquina guide →How to identify limestone
- Fizzes in dilute acid.
- Gray to cream, often with shell fossils.
- A knife scratches it.
- Weathers into smooth, pitted surfaces.
Structure: Varied, often fossiliferous
Full Limestone guide →More comparisons
Could you tell them apart from a blurry close-up?
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