Ferristrunzite is a rare hydrated iron phosphate mineral that typically forms as delicate, radiating clusters of acicular crystals in altered pegmatite deposits. Collectors usually search for these vibrant yellow to amber tufts under magnification, as they are rarely large enough for hand-specimen display.
Is this ferristrunzite?
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 ferristrunzite with a known reference. Ferristrunzite sits at Mohs 4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: very pale yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: brownish yellow, light yellow.
- 5Look at form & habitCrystal system: triclinic. Typical habit: acicular, aggregates.
Often confused with
Ferristrunzite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside ferristrunzite
Minerals reported to co-occur with ferristrunzite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- FeFe₂(PO₄)₂(OH)₃·5H₂O
- Mohs hardness
- 4
- Density
- 2.38-2.50 g/cm³
- Streak
- Very pale yellow
- Luster
- Vitreous
- Transparency
- Semitransparent
- Crystal system
- Triclinic
- Crystal habit
- Acicular, aggregates
- Cleavage
- One, probable, parallel X-Z OAP
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare secondary mineral in argillaceous and clastic sediments, probably as an oxidation product of strunzite (Blaton, Belgium)
Where rockhounds find ferristrunzite
Classic worldwide localities
- Blaton, Belgium
- Aprath, near Wuppertal, North Rhine-Westphalia, Germany
- Silbergrube quarry, near Waidhaus, Bavaria, Germany
- Ventorp, near Arnsberg, North Rhein-Westphalia, Germany
Field-hunting tip
Where it forms: A rare secondary mineral in argillaceous and clastic sediments, probably as an oxidation product of strunzite (Blaton, Belgium). If you start seeing beraunite, crandallite, diadochite in float, you are in the right ground. Typical habit: acicular, aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ferristrunzite?+
Where is ferristrunzite found?+
What rocks look like ferristrunzite?+
What minerals are found with ferristrunzite?+
What kind of rock does ferristrunzite form in?+
What is ferristrunzite used for?+
Find ferristrunzite on the map
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