Guettardite is a rare lead-arsenic sulfosalt primarily found in the famous Binn Valley of Switzerland. It typically forms as small, steel-gray metallic crystals embedded within dolomitic rocks, often requiring magnification for accurate identification due to its similarity to other sulfosalt species.

Hardness

Mohs

Luster

Metallic

Streak

Black

Transparency

Opaque

mineralrareSulfosalt Group family

Guettardite

Hardness: 3
Luster: Metallic
Streak: Black
Transparency: Opaque

No image

Is this guettardite?

5-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 guettardite with a known reference. Guettardite sits at Mohs 3 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Guettardite leaves a black streak.
3
Read the luster
Hold the specimen under a strong light. Guettardite typically shows a metallic luster.
4
Match the color range
Compare against the expected color range: lead-gray, steel-gray.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: prismatic, bladed, striated crystals.

Often confused with

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

mineral

Sartorite

Mohs 3

How to tell apart: Streak differs — Guettardite leaves black, Sartorite leaves chocolate-brown.

Often found alongside guettardite

Minerals reported to co-occur with guettardite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: PbAs₂S₄
Mohs hardness: 3
Density: 5.65 g/cm³
Colors: Lead-gray Steel-gray
Streak: Black
Luster: Metallic
Transparency: Opaque
Crystal system: Monoclinic
Crystal habit: Prismatic, Bladed, Striated Crystals
Cleavage: Good
Rarity: Rare
Uses: Collector, Scientific Research
Host rock: Dolomitic Marble Cavities
Typical price: $100-500 thumbnail

Where rockhounds find guettardite

Classic worldwide localities

Lengenbach Quarry, Switzerland
Binn Valley, Switzerland

Field-hunting tip

Look in dolomitic marble cavities country — that is the host setting where guettardite typically forms. If you start seeing sartorite, baumhauerite, realgar in float, you are in the right ground. Field specimens usually show a prismatic, bladed, striated crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify guettardite?+

Mohs hardness is 3. It typically shows a metallic luster. The streak is black. Common colors include lead-gray, steel-gray.

Where is guettardite found?+

Notable localities include Lengenbach Quarry, Switzerland; Binn Valley, Switzerland.

How much is guettardite worth?+

Typical asking prices fall in the range of $100-500 thumbnail. Quality, size, and provenance can move individual specimens well outside that range.

Is guettardite safe to handle?+

It contains toxic constituents. Contains arsenic and lead. Handle with care, wash hands after touching, and avoid creating dust. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like guettardite?+

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

What minerals are found with guettardite?+

Guettardite commonly co-occurs with Sartorite, Baumhauerite, Realgar, Pyrite, Dolomite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does guettardite form in?+

Guettardite typically forms in dolomitic marble cavities. Working float back to the host body is the standard way to chase a fresh occurrence.

What is guettardite used for?+

Guettardite is used in collector, scientific research.

Find guettardite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.