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 4-4.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: light yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: dull to resinous.
- 4Match the color rangeCompare against the expected color range: yellow, dark straw yellow, reddish brown, brown.
- 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 pale yellow; luster reads dull to resinous on Hydroniumjarosite and subadamantine to vitreous, resinous on fractures on Jarosite.
How to tell apart: Hydroniumjarosite is noticeably harder (Mohs 4-4.5 vs. 3); luster reads dull to resinous on Hydroniumjarosite and vitreous on Natrojarosite.
How to tell apart: Streak differs, so Hydroniumjarosite leaves light yellow, Goethite leaves brownish yellow, yellow-orange, ocher-yellow; luster reads dull to resinous on Hydroniumjarosite and imperfect adamantine metallic to dull earthy; silky when fibrous on Goethite.
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
- 4-4.5
- Density
- 2.50-2.90 g/cm³
- Colors
- Streak
- Light yellow
- Luster
- Dull to resinous
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Powdery, earthy, crusts, minute rhombohedral crystals
- Cleavage
- On {0001}, distinct (by analogy to jarosite)
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- In the oxidized zone of rapidly weathering sulfide-bearing rocks; may be of post-mining formation
Where rockhounds find hydroniumjarosite
Classic worldwide localities
- Black Brush deposit, Cherry Creek area, Pinal Co., Arizona, USA
- Bristol silver mine, Lincoln Co., New Mexico, USA
- Boss mine, Goodsprings district, Clark Co., Nevada, USA
- Goldstrike mine, Lynn district, and the Gold Quarry mine, near Carlin, Maggie Creek district, Eureka Co., Nevada, USA
- Staszic mine, Holy Cross Mountain, near Kielce, and at Rudawka, Rymanowska, Carpathian Mountains, Poland
- Thorez mine, Walbrzych, Lower Silesia, Poland
Field-hunting tip
Where it forms: In the oxidized zone of rapidly weathering sulfide-bearing rocks; may be of post-mining formation. If you start seeing melanterite, goethite in float, you are in the right ground. Typical habit: powdery, earthy, crusts, minute rhombohedral crystals. 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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