Dufrenoysite is a rare lead arsenic sulfosalt best known from the famous Lengenbach Quarry in the Binnental, Switzerland. It typically forms sharp, metallic, tabular crystals that often exhibit complex striations and a distinct reddish-brown streak, which helps distinguish it from other lead-gray sulfides.
Is this dufrenoysite?
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 dufrenoysite with a known reference. Dufrenoysite sits at Mohs 3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Dufrenoysite leaves a reddish-brown streak.
- 3Read the lusterHold the specimen under a strong light. Dufrenoysite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: lead-gray, iron-black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals, sometimes elongated or striated.
Often confused with
Dufrenoysite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Dufrenoysite leaves reddish-brown, Sartorite leaves chocolate-brown.
How to tell apart: Streak differs — Dufrenoysite leaves reddish-brown, Gratonite leaves black.
How to tell apart: Streak differs — Dufrenoysite leaves reddish-brown, Galena leaves lead-gray.
Often found alongside dufrenoysite
Minerals reported to co-occur with dufrenoysite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Pb₂As₂S₅
- Mohs hardness
- 3
- Density
- 5.5-5.6 g/cm³
- Colors
- Streak
- Reddish-brown
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Tabular Crystals, Sometimes Elongated or Striated
- Cleavage
- Good in One Direction
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Dolomitic Marble Cavities
- Typical price
- $50-500 thumbnail, $200-2000 cabinet
Where rockhounds find dufrenoysite
Classic worldwide localities
- Binnental, Switzerland
- Lengenbach Quarry, Switzerland
- Maderanertal, Switzerland
Field-hunting tip
Look in dolomitic marble cavities country — that is the host setting where dufrenoysite typically forms. If you start seeing realgar, orpiment, sartorite in float, you are in the right ground. Field specimens usually show a tabular crystals, sometimes elongated or striated habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find dufrenoysite on the map
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