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 ~4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: brown.
- 3Read the lusterHold the specimen under a strong light. Luster: adamantine.
- 4Match the color rangeCompare against the expected color range: 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: Hematite is the harder of the two (Mohs 5-6 vs. ~4); streak differs, so Armangite leaves brown, Hematite leaves cherry-red or reddish brown; luster reads adamantine on Armangite and metallic or submetallic to dull on Hematite.
How to tell apart: Hausmannite is the harder of the two (Mohs 5.5 vs. ~4); streak differs, so Armangite leaves brown, Hausmannite leaves dark reddish brown; 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
- Mn₂₆As₁₈O₅₀(CO₃)(OH)₄
- Mohs hardness
- ~4
- Density
- 4.43 g/cm³
- Colors
- Streak
- Brown
- Luster
- Adamantine
- Transparency
- Opaque, transparent in thin fragments
- Crystal system
- Trigonal
- Crystal habit
- Rhombohedral crystals, often with complex striated faces
- Cleavage
- {0001}, fair to poor
- Rarity
- Rare
- Uses
- Collector
- Host rock
- On a museum specimen collected from a metamorphosed Fe–Mn deposit
Where rockhounds find armangite
Classic worldwide localities
- Långban, Värmland, Sweden
Field-hunting tip
Where it forms: On a museum specimen collected from a metamorphosed Fe–Mn deposit. If you start seeing calcite, dolomite, barite in float, you are in the right ground. Typical habit: rhombohedral crystals, often with complex striated faces. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify armangite?+
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Find armangite on the map
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