Jahnsite-(CaFeMg) is a rare phosphate mineral typically found as small, yellow to brown tabular crystals within phosphate-rich zones of granite pegmatites. Collectors look for them in the vugs of altered triphylite or other primary phosphates, often requiring magnification for accurate identification.
Is this jahnsite-(cafemg)?
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-(cafemg) with a known reference. Jahnsite-(CaFeMg) 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: brownish orange.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals, sometimes in radiating aggregates.
Often found alongside jahnsite-(cafemg)
Minerals reported to co-occur with jahnsite-(cafemg). Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaFe²⁺Mg₂Fe³⁺₂(PO₄)₄(OH)₂·8H₂O
- Mohs hardness
- ~4
- Density
- 2.76 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular crystals, sometimes in radiating aggregates
- Cleavage
- Good on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A secondary mineral in low-grade phosphorites derived by leaching of weakly phosphatic limestones or low-grade primary phosphorites
Where rockhounds find jahnsite-(cafemg)
Classic worldwide localities
- Tom’s quarry, Koonunga Hill area, 10 km E of Kapunda, South Australia
Field-hunting tip
Where it forms: A secondary mineral in low-grade phosphorites derived by leaching of weakly phosphatic limestones or low-grade primary phosphorites. If you start seeing jahnsite-, goethite, fluorapatite in float, you are in the right ground. Typical habit: tabular crystals, sometimes in radiating aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify jahnsite-(cafemg)?+
Where is jahnsite-(cafemg) found?+
What minerals are found with jahnsite-(cafemg)?+
What kind of rock does jahnsite-(cafemg) form in?+
What is jahnsite-(cafemg) used for?+
Find jahnsite-(cafemg) on the map
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