Jahnsite-(MnMnMn) is a rare phosphate mineral typically found as small, yellowish-brown tabular crystals in granite pegmatites. It is often identified by its association with altered triphylite and other phosphate minerals in secondary mineral zones.
Is this jahnsite-(mnmnmn)?
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-(mnmnmn) with a known reference. Jahnsite-(MnMnMn) 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 adamantine.
- 4Match the color rangeCompare against the expected color range: yellow, brown, purplish brown, yellow orange.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals, subparallel aggregates.
Often confused with
Jahnsite-(MnMnMn) vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Jahnsite-(MnMnMn) is noticeably harder (Mohs 4 vs. 3); streak differs, so Jahnsite-(MnMnMn) leaves white, Whitmoreite leaves yellow-brown.
How to tell apart: Jahnsite-(MnMnMn) is noticeably harder (Mohs 4 vs. 3).
How to tell apart: Jahnsite-(MnMnMn) is noticeably harder (Mohs 4 vs. 3).
Often found alongside jahnsite-(mnmnmn)
Minerals reported to co-occur with jahnsite-(mnmnmn). Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- MnMnMn₂Fe₂(PO₄)₄(OH)₂·8H₂O
- Mohs hardness
- 4
- Density
- 2.66 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous to adamantine
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular crystals, subparallel aggregates
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- granite pegmatites
Where rockhounds find jahnsite-(mnmnmn)
Classic worldwide localities
- Stewart mine, Pala, San Diego County, California, USA (type locality)
Field-hunting tip
Where it forms: granite pegmatites. If you start seeing triphylite, apatite, siderite in float, you are in the right ground. Typical habit: tabular crystals, subparallel aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify jahnsite-(mnmnmn)?+
Where is jahnsite-(mnmnmn) found?+
What rocks look like jahnsite-(mnmnmn)?+
What minerals are found with jahnsite-(mnmnmn)?+
What kind of rock does jahnsite-(mnmnmn) form in?+
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Find jahnsite-(mnmnmn) on the map
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