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Jarosite
Jarosite is sulfate (alunite supergroup, iron), KFe₃(SO₄)₂(OH)₆. In the hand, it rates 2.5 to 3.5 on the Mohs scale, and it runs ochre yellow and amber brown. Mustard-ochre crusts and sparkly micro-druses in rusty mine zones, the 'yellow boy' of acid rock drainage, with a pale yellow streak.
The geology.
Jarosite carries the formula KFe₃(SO₄)₂(OH)₆. It belongs to the trigonal system. The trade files it under sulfate (alunite supergroup, iron).
It sits at 2.5 to 3.5 on the Mohs scale. The surface reads subadamantine to earthy. Light behaviour is translucent to opaque. Specific gravity runs 2.9 to 3.3. The streak is pale yellow. It breaks with distinct cleavage; uneven, crumbly.
Mustard-ochre crusts and sparkly micro-druses in rusty mine zones, the 'yellow boy' of acid rock drainage, with a pale yellow streak.
Common cuts are earthy crusts, micro-crystal druses or nodules in oxidized ore zones.
The origins.
Weathered sulfide deposits and acid mine zones worldwide: Spain (Jaroso ravine, namesake), Nevada/Arizona (USA), Australia.
On value, the database notes: field-collector specimen; inexpensive.
Traditional associations.
In energy work traditions, jarosite has little established lore; it is famous instead as a Mars-water witness mineral.
Included for completeness. Tradition is worth knowing about, and it is worth keeping separate from the mineralogy.
Spotting the real thing.
Mustard-ochre crusts and sparkly micro-druses in rusty mine zones, the 'yellow boy' of acid rock drainage, with a pale yellow streak.
| Looks like | How to tell them apart |
|---|---|
| Limonite/goethite | Goethite streaks browner; jarosite's streak is distinctly pale yellow and it forms in acid-sulfate settings |
| Sulfur | Native sulfur is brighter canary and burns-smells when warmed |
| Yellow ochre clay | Ochre is softer-staining without crystal sparkle |
At-home tests.
These checks cost nothing. Daylight, a 10x loupe and a little patience are the whole kit for jarosite.
| Test | What you should see |
|---|---|
| By eye | Pale yellow streak |
| By eye | Earthy-to-glittery crusts in oxidized sulfide zones |
| Scratch check | Soft; knife carves it |
Anything that scratches, burns or dissolves the piece is a lab job. Get it appraised rather than testing it apart.
Care & handling.
At 2.5 to 3.5 on the Mohs scale this is a soft material. Keep it as a display piece, store it apart from harder stones, and skip daily-wear settings.
It breaks with distinct cleavage; uneven, crumbly, which is worth knowing before you set it or drop it.
Warm water and a soft cloth clean almost everything. Ultrasonic tanks, steamers and household cleaners are where pieces get ruined.
A deeper look.
Extended detail on composition, sourcing, authentication and market value.
The physical record
The formula on record is KFe₃(SO₄)₂(OH)₆. Crystal system: Trigonal. Specific gravity: 2.9 to 3.3. Streak: Pale yellow. Cleavage and fracture: Distinct cleavage; uneven, crumbly.
How it reaches the market
Weathered sulfide deposits and acid mine zones worldwide: Spain (Jaroso ravine, namesake), Nevada/Arizona (USA), Australia.
What it gets confused with
Limonite/goethite: Goethite streaks browner; jarosite's streak is distinctly pale yellow and it forms in acid-sulfate settings. Sulfur: Native sulfur is brighter canary and burns-smells when warmed. Yellow ochre clay: Ochre is softer-staining without crystal sparkle.
What it is worth
Field-collector specimen; inexpensive.
One more thing
NASA's Opportunity rover found jarosite on Mars, since it needs water and acid to form, the little mineral testified to ancient Martian water.
An education-first guide.
No product links here. We do not sell jarosite, and a guide that only covers our own shelves would not be much of a guide.
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