Jahnsite-(CaMnMg) is a rare secondary phosphate mineral found primarily in complex granite pegmatites. Collectors should look for distinct, glassy, yellow-to-brown prismatic crystals often resting on weathered phosphate cores or associated with other rare phosphate species.
Is this jahnsite-(camnmg)?
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-(camnmg) with a known reference. Jahnsite-(CaMnMg) 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 to subadamantine.
- 4Match the color rangeCompare against the expected color range: yellow, brown, purplish brown, yellow orange, greenish yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular, prismatic crystals or encrusting aggregates.
Often confused with
Jahnsite-(CaMnMg) vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside jahnsite-(camnmg)
Minerals reported to co-occur with jahnsite-(camnmg). Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaMnMg₂Fe³⁺₂(PO₄)₄(OH)₂·8H₂O
- Mohs hardness
- 4
- Density
- 2.706-2.718 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous to subadamantine
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular, prismatic crystals or encrusting aggregates
- Cleavage
- Good on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A late-stage hydrothermal decomposition product of primary triphylite-lithiophilite in complex granite pegmatites
Where rockhounds find jahnsite-(camnmg)
Classic worldwide localities
- Tip Top, White Elephant, Bull Moose, Big Chief, and Linwood mines, near Custer, Custer Co., South Dakota, USA
- Sapucaia pegmatite mine, about 50 km east-southeast of Governador Valadares, Minas Gerais, Brazil
- Glen Chosaidh, Loch Quoich, Inverness-shire, Scotland
Field-hunting tip
Where it forms: A late-stage hydrothermal decomposition product of primary triphylite-lithiophilite in complex granite pegmatites. If you start seeing leucophosphite, huréaulite, collinsite in float, you are in the right ground. Typical habit: tabular, prismatic crystals or encrusting aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify jahnsite-(camnmg)?+
Where is jahnsite-(camnmg) found?+
What rocks look like jahnsite-(camnmg)?+
What minerals are found with jahnsite-(camnmg)?+
What kind of rock does jahnsite-(camnmg) form in?+
What is jahnsite-(camnmg) used for?+
Find jahnsite-(camnmg) on the map
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