Ferrostrunzite is a rare hydrated iron phosphate mineral typically found as a secondary product in oxidized phosphate-rich pegmatites. It is most commonly identified by its delicate, acicular, or needle-like yellow-brown crystal sprays that form within small vugs or cavities.
Is this ferrostrunzite?
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 ferrostrunzite with a known reference. Ferrostrunzite 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: pale brown.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: yellow brown, light brown, colorless.
- 5Look at form & habitCrystal system: triclinic. Typical habit: acicular, fibrous, radial.
Often confused with
Ferrostrunzite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Ferrostrunzite leaves pale brown, Strunzite leaves light yellow.
How to tell apart: Streak differs, so Ferrostrunzite leaves pale brown, Ferristrunzite leaves very pale yellow.
How to tell apart: Ferrostrunzite is noticeably harder (Mohs ~4 vs. 3); streak differs, so Ferrostrunzite leaves pale brown, Laueite leaves white.
Often found alongside ferrostrunzite
Minerals reported to co-occur with ferrostrunzite. 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)₂·6H₂O
- Mohs hardness
- ~4
- Density
- 2.50 g/cm³
- Streak
- Pale brown
- Luster
- Vitreous
- Transparency
- Semitransparent
- Crystal system
- Triclinic
- Crystal habit
- Acicular, fibrous, radial
- Cleavage
- Good
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Replacing a belemnite (Mullica Hill, New Jersey, USA); a secondary mineral in weathered phosphatic black shale beds (Bethel Church, Indiana, USA)
Where rockhounds find ferrostrunzite
Classic worldwide localities
- Raccoon Creek, near Mullica Hill, Gloucester Co., New Jersey, USA
- Bethel Church, Pike Co., Indiana, USA
- Dunton quarry, Newry, Oxford Co., Maine, USA
- Palermo #1 mine, near North Groton, Grafton Co., New Hampshire, USA
- Gravel Hill mine, Perranzabuloe, Cornwall, England
- Arnsberg, North Rhein-Westphalia, and Althütte and Waidhaus, Bavaria, Germany
Field-hunting tip
Where it forms: Replacing a belemnite (Mullica Hill, New Jersey, USA); a secondary mineral in weathered phosphatic black shale beds (Bethel Church, Indiana, USA). If you start seeing rockbridgeite, phosphosiderite, vivianite in float, you are in the right ground. Typical habit: acicular, fibrous, radial. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ferrostrunzite?+
Where is ferrostrunzite found?+
What rocks look like ferrostrunzite?+
What minerals are found with ferrostrunzite?+
What kind of rock does ferrostrunzite form in?+
What is ferrostrunzite used for?+
Find ferrostrunzite on the map
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