Jarosite is a hydrous potassium iron sulfate typically found as a secondary mineral in the oxidized zones of ore deposits. It is easily recognized by its distinct mustard-yellow to brownish-yellow color and earthy or crystalline habit in acidic environments.
Is this jarosite?
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 jarosite with a known reference. Jarosite 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. Jarosite leaves a yellow streak.
- 3Read the lusterHold the specimen under a strong light. Jarosite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: yellow, yellowish-brown, brown.
- 5Look at form & habitCrystal system: trigonal. Typical habit: tabular crystals, massive, granular, earthy, or encrustations.
Often confused with
Jarosite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Iron Ore is the harder of the two (Mohs 5-6.5 vs. 2.5-3.5); streak differs — Jarosite leaves yellow, Iron Ore leaves reddish-brown to black; luster reads vitreous on Jarosite and metallic to submetallic on Iron Ore.
How to tell apart: Luster reads vitreous on Jarosite and pearly on Copiapite.
How to tell apart: Streak differs — Jarosite leaves yellow, Limonite leaves yellowish-brown; luster reads vitreous on Jarosite and submetallic to earthy on Limonite.
Often found alongside jarosite
Minerals reported to co-occur with jarosite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KFe₃(SO₄)₂(OH)₆
- Mohs hardness
- 2.5-3.5
- Density
- 3.15-3.26 g/cm³
- Streak
- Yellow
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Tabular Crystals, Massive, Granular, Earthy, Or Encrustations
- Cleavage
- Distinct
- Rarity
- Common
- Uses
- Collector, Geological Indicator
- Host rock
- Oxidized Zones of Sulfide Ore Deposits
- Typical price
- $5-40 for thumbnail specimens
Where rockhounds find jarosite
5 mapped spotsClassic worldwide localities
- Rio Tinto, Spain
- Jaroso Ravine, Spain
- Cerro Gordo, USA
- Laurion, Greece
- Broken Hill, Australia
Field-hunting tip
Look in oxidized zones of sulfide ore deposits country — that is the host setting where jarosite typically forms. If you start seeing goethite, gypsum, alunite in float, you are in the right ground. Field specimens usually show a tabular crystals, massive, granular, earthy, or encrustations habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Utah, New Mexico — start trip planning there.
Common questions
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Find jarosite on the map
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