Dufrénoysite is a rare lead arsenic sulfosalt often found as distinctive lead-gray tabular crystals. It is best known for its occurrence in the famous hydrothermal cavities of the Binn Valley in Switzerland, where it often appears in complex intergrowths with other sulfosalts.
Is this dufrénoysite?
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 dufrénoysite with a known reference. Dufrénoysite 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. Dufrénoysite leaves a reddish-brown streak.
- 3Read the lusterHold the specimen under a strong light. Dufrénoysite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: lead-gray, black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals, sometimes elongated or striated.
Often confused with
Dufrénoysite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Dufrénoysite leaves reddish-brown, Sartorite leaves chocolate-brown.
How to tell apart: Streak differs — Dufrénoysite leaves reddish-brown, Baumhauerite leaves black.
How to tell apart: Streak differs — Dufrénoysite leaves reddish-brown, Galena leaves lead-gray.
Often found alongside dufrénoysite
Minerals reported to co-occur with dufrénoysite. 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
- Streak
- Reddish-brown
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Tabular Crystals, Sometimes Elongated or Striated
- Cleavage
- Good On (010)
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Dolomitic Marble Cavities
- Typical price
- $50-500 depending on crystal size and quality
Where rockhounds find dufrénoysite
2 mapped spotsClassic worldwide localities
- Binn Valley, Switzerland
- Radka mine, Bulgaria
- Jas Roux, France
Field-hunting tip
Look in dolomitic marble cavities country — that is the host setting where dufrénoysite typically forms. If you start seeing realgar, orpiment, pyrite 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. In the U.S., the densest reported localities are in Arizona, Idaho — start trip planning there.
Common questions
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Find dufrénoysite on the map
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