Hydroniumjarosite is a member of the alunite supergroup typically found as fine-grained, powdery, or crust-like coatings in acid-rich environments. It forms as a secondary mineral during the oxidation of iron-bearing sulfides and is often visually indistinguishable from other jarosite-group members without chemical analysis.
Is this hydroniumjarosite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch hydroniumjarosite with a known reference. Hydroniumjarosite sits at Mohs 2.5-3.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Hydroniumjarosite leaves a light yellow streak.
- 3Read the lusterHold the specimen under a strong light. Hydroniumjarosite typically shows a dull luster.
- 4Match the color rangeCompare against the expected color range: yellow, brownish-yellow, ochre-yellow.
- 5Look at form & habitCrystal system: trigonal. Typical habit: powdery, earthy, crusts, minute rhombohedral crystals.
Often confused with
Hydroniumjarosite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Hydroniumjarosite leaves light yellow, Jarosite leaves yellow; luster reads dull on Hydroniumjarosite and vitreous on Jarosite.
How to tell apart: Streak differs, so Hydroniumjarosite leaves light yellow, Natrojarosite leaves yellow.
How to tell apart: Iron Ore is the harder of the two (Mohs 5-6.5 vs. 2.5-3.5); streak differs, so Hydroniumjarosite leaves light yellow, Iron Ore leaves reddish-brown to black; luster reads dull on Hydroniumjarosite and metallic to submetallic on Iron Ore.
Often found alongside hydroniumjarosite
Minerals reported to co-occur with hydroniumjarosite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (H₃O)Fe₃(SO₄)₂(OH)₆
- Mohs hardness
- 2.5-3.5
- Density
- 2.9-3.0 g/cm³
- Streak
- Light Yellow
- Luster
- Dull
- Transparency
- Opaque
- Crystal system
- Trigonal
- Crystal habit
- Powdery, Earthy, Crusts, Minute Rhombohedral Crystals
- Cleavage
- None
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- Acid Mine Drainage Environments, Oxidized Zones of Sulfide Ore Deposits
- Typical price
- $10-50 for small specimens
Where rockhounds find hydroniumjarosite
Classic worldwide localities
- Rio Tinto, Spain
- Iron Mountain, California, USA
- Cerro Gordo, California, USA
Field-hunting tip
Look in acid mine drainage environments, oxidized zones of sulfide ore deposits country, the host setting where hydroniumjarosite typically forms. If you start seeing jarosite, gypsum, goethite in float, you are in the right ground. Field specimens usually show a powdery, earthy, crusts, minute rhombohedral crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find hydroniumjarosite on the map
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