Schwertmannite is an iron oxyhydroxysulfate mineral typically formed in acidic, sulfate-rich waters associated with mine drainage. It usually appears as fine-grained, yellow-brown coatings or crusts and is identified by its distinctive morphology in iron-rich oxidizing environments.
Is this schwertmannite?
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 schwertmannite with a known reference. Schwertmannite 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. Streak: ocher-yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: earthy.
- 4Match the color rangeCompare against the expected color range: brownish yellow.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: earthy, encrustations.
Often confused with
Schwertmannite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Goethite is the harder of the two (Mohs 5-5.5 vs. 2.5-3.5); streak differs, so Schwertmannite leaves ocher-yellow, Goethite leaves brownish yellow, yellow-orange, ocher-yellow; luster reads earthy on Schwertmannite and imperfect adamantine metallic to dull earthy; silky when fibrous on Goethite.
How to tell apart: Lepidocrocite is the harder of the two (Mohs 5 vs. 2.5-3.5); streak differs, so Schwertmannite leaves ocher-yellow, Lepidocrocite leaves dull orange; luster reads earthy on Schwertmannite and submetallic on Lepidocrocite.
How to tell apart: Streak differs, so Schwertmannite leaves ocher-yellow, Jarosite leaves pale yellow; luster reads earthy on Schwertmannite and subadamantine to vitreous, resinous on fractures on Jarosite.
Often found alongside schwertmannite
Minerals reported to co-occur with schwertmannite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe₈O₈(OH)₆(SO₄)·nH₂O
- Mohs hardness
- 2.5-3.5
- Density
- 3.77-3.99 g/cm³
- Colors
- Streak
- Ocher-yellow
- Luster
- Earthy
- Transparency
- Semitransparent
- Crystal system
- Tetragonal
- Crystal habit
- Earthy, encrustations
- Cleavage
- None
- Rarity
- Common
- Uses
- Collector, Scientific research
- Host rock
- A secondary mineral precipitated by waters of pH 3–4.5 and high in iron sulfate content from the surface oxidation of metal sulfides
Where rockhounds find schwertmannite
Classic worldwide localities
- Pyhäsalmi mine, Oulu, Finland
- Over 40 unspecified localities in Europe, North America, and Australia
Field-hunting tip
Where it forms: A secondary mineral precipitated by waters of pH 3–4.5 and high in iron sulfate content from the surface oxidation of metal sulfides. If you start seeing goethite, jarosite, natrojarosite in float, you are in the right ground. Typical habit: earthy, encrustations. Train your eye for that shape before scanning the outcrop.
Common questions
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Find schwertmannite on the map
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