Lengenbachite is an exceptionally rare sulfosalt mineral primarily known from the famous Lengenbach locality in the Binntal valley of Switzerland. It typically occurs as thin, lead-gray lath-like or platy crystals embedded within dolomitic marble, often requiring microscopic study for positive identification. It is highly prized by collectors of rare minerals, especially those focused on complex sulfide and sulfosalt assemblages.
Is this lengenbachite?
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 lengenbachite with a known reference. Lengenbachite sits at Mohs 1.5-2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: brown-black.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: gray blue, steel gray.
- 5Look at form & habitCrystal system: triclinic. Typical habit: tabular.
Often confused with
Lengenbachite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Jordanite is the harder of the two (Mohs 3 vs. 1.5-2); streak differs, so Lengenbachite leaves brown-black, Jordanite leaves black.
How to tell apart: Sartorite is the harder of the two (Mohs 3 vs. 1.5-2); streak differs, so Lengenbachite leaves brown-black, Sartorite leaves chocolate-brown.
Often found alongside lengenbachite
Minerals reported to co-occur with lengenbachite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ag₄Cu₂Pb₁₈As₁₂S₃₉
- Mohs hardness
- 1.5-2
- Density
- 5.80-5.85 g/cm³
- Colors
- Streak
- Brown-black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Triclinic
- Crystal habit
- Tabular
- Cleavage
- Perfect on {100}; two others across the flat {100} face
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Of hydrothermal origin
Where rockhounds find lengenbachite
Classic worldwide localities
- Lengenbach quarry, Binntal, Valais, Switzerland (type locality)
Field-hunting tip
Where it forms: Of hydrothermal origin. If you start seeing pyrite, sphalerite, jordanite in float, you are in the right ground. Typical habit: tabular. Train your eye for that shape before scanning the outcrop.
Common questions
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Find lengenbachite on the map
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