Dufrénite is a phosphate mineral commonly found in radial, botryoidal, or fibrous crusts with a distinct dark green color. It forms in the oxidized zones of phosphate-bearing pegmatites and is often associated with other secondary phosphate minerals.
Is this dufrénite?
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 dufrénite with a known reference. Dufrénite sits at Mohs 3.5-4.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: green.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to silky.
- 4Match the color rangeCompare against the expected color range: dark green, brown, greenish brown, green black, olive green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: fibrous, massive, radial.
Often confused with
Dufrénite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Dufrénite is noticeably harder (Mohs 3.5-4.5 vs. 1.5-2); streak differs, so Dufrénite leaves green, Vivianite leaves white, altering to dark blue, brown.
How to tell apart: Streak differs, so Dufrénite leaves green, Strengite leaves white.
Often found alongside dufrénite
Minerals reported to co-occur with dufrénite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₀.₅FeFe₅(PO₄)₄(OH)₆·2H₂O
- Mohs hardness
- 3.5-4.5
- Density
- 3.1-3.34 g/cm³
- Colors
- Streak
- Green
- Luster
- Vitreous to silky
- Transparency
- Translucent to almost opaque
- Crystal system
- Monoclinic
- Crystal habit
- Fibrous, massive, radial
- Cleavage
- Perfect; distinct
- Rarity
- Uncommon
- Uses
- Collector, Mineralogical specimen
- Host rock
- A secondary mineral formed principally in iron ore deposits
Where rockhounds find dufrénite
Classic worldwide localities
- Rock Run, Cherokee Co., Alabama, USA
- Palermo #1 mine, near North Groton, Grafton Co., New Hampshire, USA
- Tip Top mine, 8.5 km southwest of Custer, Custer Co., South Dakota, USA
- Sequoia Pit, Iron Point district, Humboldt Co., and in the Gold Quarry mine, near Carlin, Maggie Creek district, Eureka Co., Nevada, USA
- Hirschberg, Ullersreuth, and Lobenstein, Thuringia, Germany
- Hauptmannsgrün, near Reichenbach, Saxony, Germany
Field-hunting tip
Where it forms: A secondary mineral formed principally in iron ore deposits. If you start seeing goethite, beraunite, quartz in float, you are in the right ground. Typical habit: fibrous, massive, radial. Train your eye for that shape before scanning the outcrop.
Common questions
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Find dufrénite on the map
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