Stalderite is an exceptionally rare thallium-bearing sulfosalt mineral found primarily in the famous Lengenbach Quarry in Switzerland. It typically occurs as small, metallic lead-gray tabular crystals nestled within complex dolomite-hosted hydrothermal deposits.
Is this stalderite?
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 stalderite with a known reference. Stalderite sits at Mohs 3.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Stalderite leaves a black streak.
- 3Read the lusterHold the specimen under a strong light. Stalderite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: lead-gray, black.
- 5Look at form & habitCrystal system: trigonal. Typical habit: tabular crystals.
Often confused with
Stalderite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Stalderite leaves black, Sartorite leaves chocolate-brown.
How to tell apart: Stalderite is noticeably harder (Mohs 3.5 vs. 1.5-2); streak differs — Stalderite leaves black, Smithite leaves orange-red; luster reads metallic on Stalderite and adamantine on Smithite.
Often found alongside stalderite
Minerals reported to co-occur with stalderite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CuZn₂TlAs₃S₆
- Mohs hardness
- 3.5
- Density
- 5.45 g/cm³
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Trigonal
- Crystal habit
- Tabular Crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Dolomite Rocks in Hydrothermal Deposits
- Typical price
- $200-1500 per specimen depending on size and quality
Where rockhounds find stalderite
Classic worldwide localities
- Lengenbach Quarry, Binntal, Switzerland
Field-hunting tip
Look in dolomite rocks in hydrothermal deposits country — that is the host setting where stalderite typically forms. If you start seeing lengenbachite, realgar, orpiment in float, you are in the right ground. Field specimens usually show a tabular crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find stalderite on the map
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