Gengenbachite is a rare potassium iron phosphate. It was approved as a distinct mineral species in 2001, from material found at the Silberbrünnle mine, Haigerach valley near Gengenbach, central Black Forest, Germany.
Is this gengenbachite?
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 gengenbachite with a known reference. Gengenbachite 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. Gengenbachite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Gengenbachite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white.
- 5Look at form & habitCrystal system: trigonal. Typical habit: tabular crystals.
Often confused with
Gengenbachite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside gengenbachite
Minerals reported to co-occur with gengenbachite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KFe₃(H₂PO₄)₂(HPO₄)₄·6H₂O
- Mohs hardness
- 2
- Density
- 2.47 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Trigonal
- Crystal habit
- Tabular Crystals
- Cleavage
- Perfect Basal
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Associated with Organic-rich Soils in Protected Cave Environments
Where rockhounds find gengenbachite
Classic worldwide localities
- Gengenbach, Black Forest, Germany
Field-hunting tip
Look in associated with organic-rich soils in protected cave environments country, the host setting where gengenbachite typically forms. If you start seeing oxammite in float, you are in the right ground. Field specimens usually show a tabular crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify gengenbachite?+
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What rocks look like gengenbachite?+
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Find gengenbachite on the map
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