Jahnsite-(NaFeMg) is a rare secondary phosphate mineral found primarily in altered phosphate-rich granite pegmatites. Collectors typically look for small, distinct yellow-to-brown tabular crystals occurring in vugs associated with other phosphate minerals.
Is this jahnsite-(nafemg)?
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-(nafemg) with a known reference. Jahnsite-(NaFeMg) 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: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic, striated.
Often confused with
Jahnsite-(NaFeMg) vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside jahnsite-(nafemg)
Minerals reported to co-occur with jahnsite-(nafemg). Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- NaFe²⁺Mg₂Fe³⁺₂(PO₄)₄(OH)₂·8H₂O
- Mohs hardness
- 4
- Density
- 2.58 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic, striated
- Cleavage
- Good on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A late-stage hydrothermal decomposition product of triphylite in a complex granitic pegmatite
Where rockhounds find jahnsite-(nafemg)
Classic worldwide localities
- Tip Top mine, Custer County, South Dakota, USA
Field-hunting tip
Where it forms: A late-stage hydrothermal decomposition product of triphylite in a complex granitic pegmatite. If you start seeing heterosite, leucophosphite, dufrénite in float, you are in the right ground. Typical habit: prismatic, striated. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify jahnsite-(nafemg)?+
Where is jahnsite-(nafemg) found?+
What rocks look like jahnsite-(nafemg)?+
What minerals are found with jahnsite-(nafemg)?+
What kind of rock does jahnsite-(nafemg) form in?+
What is jahnsite-(nafemg) used for?+
Find jahnsite-(nafemg) on the map
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