Siderotil is a secondary sulfate mineral that typically forms as an efflorescent crust or fibrous coating on rock surfaces in mine workings. It is chemically unstable and dehydration-prone, often requiring careful storage to prevent it from turning into a white powder as it alters to rozenite.
Is this siderotil?
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 siderotil with a known reference. Siderotil sits at Mohs 2.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Siderotil leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Siderotil typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, pale blue, pale green.
- 5Look at form & habitCrystal system: triclinic. Typical habit: fibrous, efflorescent crusts, powdery coatings.
Often confused with
Siderotil vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside siderotil
Minerals reported to co-occur with siderotil. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Fe,Cu)SO₄·5H₂O
- Mohs hardness
- 2.5
- Density
- 1.97 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Triclinic
- Crystal habit
- Fibrous, Efflorescent Crusts, Powdery Coatings
- Cleavage
- None
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- Oxidized Zones of Sulfide Ore Deposits
- Typical price
- $10-60 for small specimens
Where rockhounds find siderotil
Classic worldwide localities
- Rio Tinto, Spain
- Bisbee, Arizona, USA
- Chuquicamata, Chile
- Rammelsberg, Germany
Field-hunting tip
Look in oxidized zones of sulfide ore deposits country, the host setting where siderotil typically forms. If you start seeing melanterite, chalcanthite, pyrite in float, you are in the right ground. Field specimens usually show a fibrous, efflorescent crusts, powdery coatings habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify siderotil?+
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How much is siderotil worth?+
What rocks look like siderotil?+
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Find siderotil on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
