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 2 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Humboldtine leaves a yellowish-white streak.
- 3Read the lusterHold the specimen under a strong light. Humboldtine typically shows a resinous luster.
- 4Match the color rangeCompare against the expected color range: yellow, brownish-yellow, amber-yellow.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: short prismatic crystals, fibrous aggregates, massive.
Often confused with
Humboldtine vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Humboldtine leaves yellowish-white, Whewellite leaves white; luster reads resinous on Humboldtine and vitreous on Whewellite.
How to tell apart: Weddellite is the harder of the two (Mohs 3.5 vs. 2); streak differs — Humboldtine leaves yellowish-white, Weddellite leaves white; luster reads 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
- 2
- Density
- 2.29 g/cm³
- Streak
- Yellowish-white
- Luster
- Resinous
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Short Prismatic Crystals, Fibrous Aggregates, Massive
- Cleavage
- Perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Brown Coal Deposits, Hydrothermal Mineral Veins
- Typical price
- $20-150 thumbnail, $200+ cabinet specimen
Where rockhounds find humboldtine
Classic worldwide localities
- Kolin, Czech Republic
- Schwarzenberg, Germany
- Kassel, Germany
- Krivoy Rog, Ukraine
Field-hunting tip
Look in brown coal deposits, hydrothermal mineral veins country — that is the host setting where humboldtine typically forms. If you start seeing limonite, goethite, siderite in float, you are in the right ground. Field specimens usually show a short prismatic crystals, fibrous aggregates, massive habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find humboldtine on the map
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