Gjerdingenite-Mn is a rare member of the labuntsovite group typically found as small, brown to red-brown prismatic crystals in alkaline igneous environments. It is most famous from the complex pegmatites of the Langesundsfjord region in Norway, often occurring as a late-stage crystallization product.
Is this gjerdingenite-mn?
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 gjerdingenite-mn with a known reference. Gjerdingenite-Mn sits at Mohs 5, 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: orange yellow, brownish yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic.
Often confused with
Gjerdingenite-Mn vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Labuntsovite is the harder of the two (Mohs 6 vs. 5); luster reads vitreous on Gjerdingenite-Mn and greasy on Labuntsovite.
How to tell apart: Gjerdingenite-Mn is noticeably harder (Mohs 5 vs. 3-4); streak differs, so Gjerdingenite-Mn leaves white, Kupletskite leaves brown.
Often found alongside gjerdingenite-mn
Minerals reported to co-occur with gjerdingenite-mn. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- K₂Mn(Ti,Nb)₄(Si₄O₁₂)₂(OH,O)₄·n(H₂O)
- Mohs hardness
- 5
- Density
- 2.93 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In miarolitic cavities, with little or no late-stage hydrothermal alteration, in a sodic alkaline granite
Where rockhounds find gjerdingenite-mn
Classic worldwide localities
- Gjerdingselva, Lunner, Oppland, Norway
Field-hunting tip
Where it forms: In miarolitic cavities, with little or no late-stage hydrothermal alteration, in a sodic alkaline granite. If you start seeing gjerdingenite-fe, aegirine, albite in float, you are in the right ground. Typical habit: prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
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