Wilhelmgümbelite is a rare secondary phosphate mineral typically found as a result of the alteration of triphylite in granitic pegmatites. Collectors should look for small, delicate platy crystals or radiating sprays in the cavities of weathered phosphate zones. It is named in honor of the German geologist Wilhelm von Gümbel.
Is this wilhelmgümbelite?
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 wilhelmgümbelite with a known reference. Wilhelmgümbelite sits at Mohs 3-4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: pale yellow-brown.
- 3Read the lusterHold the specimen under a strong light. Luster: dull.
- 4Match the color rangeCompare against the expected color range: orange-red.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: platy crystals, radial aggregates, crusts.
Often confused with
Wilhelmgümbelite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Wilhelmgümbelite leaves pale yellow-brown, Hopeite leaves white; luster reads dull on Wilhelmgümbelite and vitreous, pearly on {010} cleavages on Hopeite.
How to tell apart: Streak differs, so Wilhelmgümbelite leaves pale yellow-brown, Parahopeite leaves white; luster reads dull on Wilhelmgümbelite and vitreous, pearly on cleavages on Parahopeite.
How to tell apart: Streak differs, so Wilhelmgümbelite leaves pale yellow-brown, Phosphophyllite leaves white; luster reads dull on Wilhelmgümbelite and vitreous on Phosphophyllite.
Often found alongside wilhelmgümbelite
Minerals reported to co-occur with wilhelmgümbelite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- ZnFeFe₃(PO₄)₃(OH)₄(H₂O)₅·2H₂O
- Mohs hardness
- 3-4
- Density
- 2.89 g/cm³
- Colors
- Streak
- Pale yellow-brown
- Luster
- Dull
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Platy crystals, radial aggregates, crusts
- Cleavage
- Perfect on {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In the highly oxidized portion of a phosphate-bearing granitic pegmatite, probably formed from schoonerite by replacement reactions (enrichment of Zn and Fe, depletion of Mn) together with oxidation of Fe2+ to Fe3+
Where rockhounds find wilhelmgümbelite
Classic worldwide localities
- Found on the 67 m level, Cornelia open-cut mine, Hagendorf-Süd pegmatite, Hagendorf, Oberpfalz, Bavaria, Germany
Field-hunting tip
Where it forms: In the highly oxidized portion of a phosphate-bearing granitic pegmatite, probably formed from schoonerite by replacement reactions (enrichment of Zn and Fe, depletion of Mn) together with oxidation of Fe2+ to Fe3+. If you start seeing albite, sr-bearing apatite, chalcophanite in float, you are in the right ground. Typical habit: platy crystals, radial aggregates, crusts. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify wilhelmgümbelite?+
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What rocks look like wilhelmgümbelite?+
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Find wilhelmgümbelite on the map
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