Armangite is a very rare manganese-arsenic mineral known almost exclusively from the famous Långban mines in Sweden. It typically appears as small, complex black rhombohedral crystals that exhibit a distinct adamantine luster.
Is this armangite?
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 armangite with a known reference. Armangite sits at Mohs 3.5-4 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Armangite leaves a brown streak.
- 3Read the lusterHold the specimen under a strong light. Armangite typically shows a adamantine luster.
- 4Match the color rangeCompare against the expected color range: black, brownish-black.
- 5Look at form & habitCrystal system: trigonal. Typical habit: rhombohedral crystals, often with complex striated faces.
Often confused with
Armangite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Iron Ore is the harder of the two (Mohs 5-6.5 vs. 3.5-4); streak differs — Armangite leaves brown, Iron Ore leaves reddish-brown to black; luster reads adamantine on Armangite and metallic to submetallic on Iron Ore.
How to tell apart: Hausmannite is the harder of the two (Mohs 5-5.5 vs. 3.5-4); streak differs — Armangite leaves brown, Hausmannite leaves brownish-red; luster reads adamantine on Armangite and submetallic on Hausmannite.
Often found alongside armangite
Minerals reported to co-occur with armangite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mn²⁺₂₆As⁶⁺₆As³⁺₆O₄₈(OH)₄
- Mohs hardness
- 3.5-4
- Density
- 4.2 g/cm³
- Colors
- Streak
- Brown
- Luster
- Adamantine
- Transparency
- Opaque
- Crystal system
- Trigonal
- Crystal habit
- Rhombohedral Crystals, Often with Complex Striated Faces
- Cleavage
- Perfect On {0001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Metamorphosed Iron-manganese Ore Deposits
- Typical price
- $50-500 depending on specimen size and quality
Where rockhounds find armangite
Classic worldwide localities
- Långban, Värmland, Sweden
Field-hunting tip
Look in metamorphosed iron-manganese ore deposits country — that is the host setting where armangite typically forms. If you start seeing barite, calcite, dixenite in float, you are in the right ground. Field specimens usually show a rhombohedral crystals, often with complex striated faces habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find armangite on the map
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