Trigonite is a rare lead-manganese arsenite mineral found almost exclusively in the famous Långban mining district of Sweden. It typically occurs as small, pale yellow to brownish-yellow tabular crystals or aggregates within manganese-rich skarns.
Is this trigonite?
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 trigonite with a known reference. Trigonite sits at Mohs 2.5-3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Trigonite leaves a light yellow streak.
- 3Read the lusterHold the specimen under a strong light. Trigonite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: yellow, yellowish-brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals.
Often confused with
Trigonite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Trigonite leaves light yellow, Mimetite leaves white; luster reads vitreous on Trigonite and adamantine on Mimetite.
How to tell apart: Streak differs — Trigonite leaves light yellow, Hectorite leaves white; luster reads vitreous on Trigonite and earthy on Hectorite.
Often found alongside trigonite
Minerals reported to co-occur with trigonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Pb₃Mn(AsO₃)₂(OH)₂
- Mohs hardness
- 2.5-3
- Density
- 4.26 g/cm³
- Colors
- Streak
- Light Yellow
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular Crystals
- Cleavage
- Perfect On {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Metamorphosed Iron-manganese Ore Deposits
- Typical price
- $50-500 depending on crystal size and quality
Where rockhounds find trigonite
Classic worldwide localities
- Långban, Sweden
- Jakobsberg, Sweden
Field-hunting tip
Look in metamorphosed iron-manganese ore deposits country — that is the host setting where trigonite typically forms. If you start seeing långbanite, hausmannite, barite in float, you are in the right ground. Field specimens usually show a tabular crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify trigonite?+
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Find trigonite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
