Gudmundite is a relatively uncommon iron antimony sulfide that typically appears as metallic, steel-gray masses. It is most easily identified in laboratory settings due to its striking resemblance to arsenopyrite, though it is often found in antimony-rich ore deposits rather than simple arsenic veins.
Is this gudmundite?
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 gudmundite with a known reference. Gudmundite sits at Mohs 6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Gudmundite leaves a dark gray to black streak.
- 3Read the lusterHold the specimen under a strong light. Gudmundite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: silver-white, steel-gray, creamy-white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: massive, granular, or rarely as distinct prismatic crystals.
Often confused with
Gudmundite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside gudmundite
Minerals reported to co-occur with gudmundite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- FeSbS
- Mohs hardness
- 6
- Density
- 6.9 g/cm³
- Streak
- Dark Gray to Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Massive, Granular, Or Rarely as Distinct Prismatic Crystals
- Cleavage
- None
- Rarity
- Uncommon
- Uses
- Collector, Scientific Research
- Host rock
- Hydrothermal Veins, Contact Metamorphic Deposits
- Typical price
- $20-100 per specimen depending on size and association
Where rockhounds find gudmundite
Classic worldwide localities
- Gudmundstorp, Sweden
- Broken Hill, Australia
- Boliden, Sweden
- Yellowknife, Canada
Field-hunting tip
Look in hydrothermal veins, contact metamorphic deposits country, the host setting where gudmundite typically forms. If you start seeing arsenopyrite, galena, sphalerite in float, you are in the right ground. Field specimens usually show a massive, granular, or rarely as distinct prismatic crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find gudmundite on the map
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