RocksdayIronstone vs Limonite
How to tell them apart
Sedimentary rock rich in iron minerals such as siderite, goethite or hematite.
Photo: James St. John, CC BY-SA 4.0
A rusty mixture of hydrated iron oxides, not a single mineral. It forms where iron-rich rocks weather.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
Quick tests
- Texture: Ironstone is a rock — a mix of grains or minerals; Limonite is a single mineraloid.
Key differences
- Limonite is the earthy iron oxide itself.
Side by side
| Property | Ironstone | Limonite |
|---|---|---|
| Type | Sedimentary rock | Mineraloid |
| Mohs hardness | 4–6 | 4–5.5 |
| Luster | Dull | Earthy to dull |
| Streak | — | Yellowish brown |
| Colors | Brown, Red, Orange | Brown, Yellow, Orange |
| Crystal system / structure | Iron-rich sedimentary | Amorphous mixture |
| Specific gravity | 3–3.6 | 2.7–4.3 |
| Formula | — | FeO(OH)·nH₂O |
| Found in | Cleveland Hills, England; Birmingham, Alabama | Bogs and weathered iron deposits worldwide |
Properties that are the same for both are grayed out.
How to identify ironstone
- Heavy, rusty brown to red.
- Often forms nodules or layers in shale.
- Rusty-brown streak.
Structure: Iron-rich sedimentary
Full Ironstone guide →How to identify limonite
- Rusty yellow-brown, earthy masses.
- Yellowish-brown streak.
- Often fills holes or replaces pyrite cubes.
Structure: Amorphous mixture
Full Limonite guide →More comparisons
Could you tell them apart from a blurry close-up?
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