Humboldtine is a rare iron oxalate mineral typically found in sedimentary brown coal deposits or specific hydrothermal vein environments. It is characterized by its distinct yellow color and low hardness, and collectors should handle specimens carefully due to its fragile and slightly water-soluble nature.
Is this humboldtine?
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 humboldtine with a known reference. Humboldtine sits at Mohs 1.5-2, 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, brownish yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic.
Often confused with
Humboldtine vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Humboldtine leaves light yellow, Whewellite leaves white; luster reads dull to resinous on Humboldtine and vitreous, pearly on {010} and some cleavages on Whewellite.
How to tell apart: Weddellite is the harder of the two (Mohs ~4 vs. 1.5-2); streak differs, so Humboldtine leaves light yellow, Weddellite leaves white; luster reads dull to resinous on Humboldtine and vitreous on Weddellite.
Often found alongside humboldtine
Minerals reported to co-occur with humboldtine. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- FeC₂O₄·2H₂O
- Mohs hardness
- 1.5-2
- Density
- 2.28 g/cm³
- Colors
- Streak
- Light yellow
- Luster
- Dull to resinous
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic
- Cleavage
- {110}, perfect; {100} and {010}, imperfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Typically coating fractures in brown coal deposits; very rarely in granite pegmatites and hydrothermal mineral deposits
Where rockhounds find humboldtine
Classic worldwide localities
- Korozluky (Korozoluk), southwest of Bílina (Bilin), at Čermniky (Tschermig), Lužice (Luschitz), and Lomnice, near Sokolov (Lant, near Falkenau), Czech Republic
- Grossalmerode, Hesse, Germany
- Potschappel, south of Dresden, Saxony, Germany
- Sailauf, northeast of Aschaffenburg, Spessart Mountains, Bavaria, Germany
- Pendarves mine, Camborne, Cornwall, England
- Capo d’Arco and Capo Calamita, Elba, Italy
Field-hunting tip
Where it forms: Typically coating fractures in brown coal deposits; very rarely in granite pegmatites and hydrothermal mineral deposits. If you start seeing gypsum, tschermigite, cassiterite in float, you are in the right ground. Typical habit: prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify humboldtine?+
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What rocks look like humboldtine?+
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Find humboldtine on the map
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