RocksdayJarosite vs Limonite
How to tell them apart
A yellow-brown iron sulfate formed where sulfide minerals weather in acidic water.
Photo: Dave Dyet http://www.shutterstone.com http://www.dyet.com, Public domain
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
- Hardness: Limonite is clearly harder: Mohs 4–5.5 versus 2.5–3.5.
- Streak (rub on unglazed porcelain): Jarosite leaves a pale yellow streak; Limonite leaves yellowish brown.
Key differences
- Limonite is browner and earthy.
Side by side
| Property | Jarosite | Limonite |
|---|---|---|
| Type | Mineral | Mineraloid |
| Mohs hardness | 2.5–3.5 | 4–5.5 |
| Luster | Subadamantine to dull | Earthy to dull |
| Streak | Pale yellow | Yellowish brown |
| Colors | Yellow, Brown | Brown, Yellow, Orange |
| Crystal system / structure | Trigonal | Amorphous mixture |
| Specific gravity | 2.9–3.3 | 2.7–4.3 |
| Formula | KFe₃(SO₄)₂(OH)₆ | FeO(OH)·nH₂O |
| Found in | Barranco Jaroso, Spain; Utah | Bogs and weathered iron deposits worldwide |
Properties that are the same for both are grayed out.
How to identify jarosite
- Mustard-yellow to brown crusts of tiny crystals.
- Pale yellow streak.
- Often with weathered pyrite.
Crystal system: Trigonal
Full Jarosite 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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