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.

Hardness

3.5-4

Mohs

Luster

Metallic

Transparency

Opaque

mineralrareSartorite Group family

Stalderite

Hardness: 3.5-4
Luster: Metallic
Transparency: Opaque

Is this stalderite?

4-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch stalderite with a known reference. Stalderite sits at Mohs 3.5-4, softer than the next harder reference, harder than the previous one.
2
Read the luster
Hold the specimen under a strong light. Luster: metallic.
3
Match the color range
Compare against the expected color range: black, reddish black, bluish black.
4
Look at form & habit
Crystal system: tetragonal. Typical habit: crystalline, euhedral crystals.

Often confused with

Stalderite vs. its common look-alikes, and how to tell them apart in the field.

How to tell apart: Stalderite is noticeably harder (Mohs 3.5-4 vs. 1.5-2); luster reads metallic on Stalderite and adamantine on Smithite.

Compare →

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: TlCu(Zn,Fe,Hg)₂As₂S₆
Mohs hardness: 3.5-4
Density: 4.97 g/cm³
Colors: Black Reddish black Bluish black
Luster: Metallic
Transparency: Opaque
Crystal system: Tetragonal
Crystal habit: Crystalline, euhedral crystals
Rarity: Rare
Uses: Collector
Host rock: All rights reserved

Where rockhounds find stalderite

Classic worldwide localities

Lengenbach, Binntal, Canton Wallis, Switzerland (type locality)

Field-hunting tip

Where it forms: All rights reserved. If you start seeing lengenbachite, realgar, orpiment in float, you are in the right ground. Typical habit: crystalline, euhedral crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify stalderite?+

Mohs hardness is 3.5-4. Luster: metallic. Common colors include black, reddish black, bluish black.

Where is stalderite found?+

Notable localities include Lengenbach, Binntal, Canton Wallis, Switzerland (type locality).

Is stalderite safe to handle?+

Stalderite contains arsenic, copper, mercury and thallium and calls for real care. Contains arsenic and thallium, both highly toxic elements; handle with care and wash hands thoroughly after contact.

What rocks look like stalderite?+

Stalderite is most often confused with Sartorite, Smithite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with stalderite?+

Stalderite commonly co-occurs with Lengenbachite, Realgar, Orpiment, Pyrite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does stalderite form in?+

What is stalderite used for?+

Stalderite is used in collector.

Find stalderite on the map

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