Jahnsite-(MnMnFe) is a rare secondary phosphate mineral typically found in complex granite pegmatites. Collectors should look for small, sharp, yellow to brownish-orange crystals perched in vugs alongside other rare phosphate minerals.
Is this jahnsite-(mnmnfe)?
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 jahnsite-(mnmnfe) with a known reference. Jahnsite-(MnMnFe) 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 greenish brown.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: dark orange-brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular to prismatic crystals, often as crusts or crystalline aggregates.
Often confused with
Jahnsite-(MnMnFe) vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Jahnsite-(MnMnFe) leaves pale greenish brown, Strengite leaves white.
How to tell apart: Streak differs, so Jahnsite-(MnMnFe) leaves pale greenish brown, Rockbridgeite leaves greenish gray.
How to tell apart: Streak differs, so Jahnsite-(MnMnFe) leaves pale greenish brown, Phosphosiderite leaves white.
Often found alongside jahnsite-(mnmnfe)
Minerals reported to co-occur with jahnsite-(mnmnfe). Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- MnMnFe₂Fe₂(PO₄)₄(OH)₂·8H₂O
- Mohs hardness
- ~4
- Density
- 2.654 g/cm³
- Colors
- Dark orange-brown
- Streak
- Pale greenish brown
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular to prismatic crystals, often as crusts or crystalline aggregates
- Cleavage
- Perfect on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A low temperature, secondary mineral formed by alteration of primary phosphates in zoned granitic pegmatite
Where rockhounds find jahnsite-(mnmnfe)
Classic worldwide localities
- Tip Top mine, South Dakota, USA
- Big Chief mine, South Dakota, USA
- Hagendorf, Bavaria, Germany
- Mangualde, Viseu, Portugal
Field-hunting tip
Where it forms: A low temperature, secondary mineral formed by alteration of primary phosphates in zoned granitic pegmatite. If you start seeing rockbridgeite, mitridatite in float, you are in the right ground. Typical habit: tabular to prismatic crystals, often as crusts or crystalline aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify jahnsite-(mnmnfe)?+
Where is jahnsite-(mnmnfe) found?+
What rocks look like jahnsite-(mnmnfe)?+
What minerals are found with jahnsite-(mnmnfe)?+
What kind of rock does jahnsite-(mnmnfe) form in?+
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Find jahnsite-(mnmnfe) on the map
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