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. Streak: reddish brown to chocolate-brown.
- 3Read the lusterHold the specimen under a strong light. Luster: submetallic.
- 4Match the color rangeCompare against the expected color range: lead gray, gray, steel gray.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: massive.
Often confused with
Dufrénoysite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Dufrénoysite leaves reddish brown to chocolate-brown, Sartorite leaves chocolate-brown; luster reads submetallic on Dufrénoysite and metallic on Sartorite.
How to tell apart: Streak differs, so Dufrénoysite leaves reddish brown to chocolate-brown, Baumhauerite leaves chocolate-brown; luster reads submetallic on Dufrénoysite and metallic on Baumhauerite.
How to tell apart: Streak differs, so Dufrénoysite leaves reddish brown to chocolate-brown, Galena leaves lead-gray; luster reads submetallic on Dufrénoysite and metallic on Galena.
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
- 5.50-5.57 g/cm³
- Colors
- Streak
- Reddish brown to chocolate-brown
- Luster
- Submetallic
- Transparency
- Subtranslucent
- Crystal system
- Monoclinic
- Crystal habit
- Massive
- Cleavage
- {010}, perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- An uncommon mineral of medium- to low-temperature hydrothermal origin
Where rockhounds find dufrénoysite
2 mapped spotsClassic worldwide localities
- Silver Star claims, near Fruitland, Stevens Co., Washington, and at the Zuni mine, San Juan Co., Colorado, USA
- Binntal, Valais, in the Lengenbach quarry (type locality), and at Recki Bach, Switzerland
- Bleikvassli Zn–Pb–Cu deposit, Nordland, Norway
- Wheal Boys, St. Endellion, Cornwall, England
- Hemlo gold deposit, Thunder Bay district, Ontario, Canada
Field-hunting tip
Where it forms: An uncommon mineral of medium- to low-temperature hydrothermal origin. If you start seeing chalcopyrite, sphalerite, realgar in float, you are in the right ground. Typical habit: massive. 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.
More dufrénoysite photos
Common questions
How do you identify dufrénoysite?+
Where is dufrénoysite found?+
Can I find dufrénoysite in the United States?+
Is dufrénoysite safe to handle?+
What rocks look like dufrénoysite?+
What minerals are found with dufrénoysite?+
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Find dufrénoysite on the map
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