Marumoite is a rare lead-arsenic sulfosalt mineral found almost exclusively in the famous Lengenbach Quarry in the Binntal of Switzerland. Collectors prize it for its metallic, lead-grey prismatic crystals that are often heavily striated and found embedded in dolomitic marble.

Hardness

Mohs

Luster

Metallic

Streak

Black

Transparency

Opaque

mineralrareSartorite Group family

Marumoite

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

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Is this marumoite?

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 marumoite with a known reference. Marumoite 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. Marumoite leaves a black streak.
3
Read the luster
Hold the specimen under a strong light. Marumoite typically shows a metallic luster.
4
Match the color range
Compare against the expected color range: lead-gray, black.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: prismatic crystals, striated.

Often confused with

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

mineral

Sartorite

Mohs 3

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

Often found alongside marumoite

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

All properties

Chemical formula: Pb₈As₁₂S₂₈
Mohs hardness: 3
Density: 5.68 g/cm³
Colors: Lead-gray Black
Streak: Black
Luster: Metallic
Transparency: Opaque
Crystal system: Monoclinic
Crystal habit: Prismatic Crystals, Striated
Cleavage: Good On {010}
Rarity: Rare
Uses: Collector
Host rock: Dolomitic Marble
Typical price: $50-500 thumbnail

Where rockhounds find marumoite

Classic worldwide localities

Lengenbach Quarry, Binn, Switzerland

Field-hunting tip

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

Common questions

How do you identify marumoite?+

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

Where is marumoite found?+

Notable localities include Lengenbach Quarry, Binn, Switzerland.

How much is marumoite worth?+

Typical asking prices fall in the range of $50-500 thumbnail. Quality, size, and provenance can move individual specimens well outside that range.

Is marumoite safe to handle?+

It contains toxic constituents. Contains lead and arsenic; avoid inhalation of dust and wash hands thoroughly after handling. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like marumoite?+

Marumoite 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 marumoite?+

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

What kind of rock does marumoite form in?+

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

What is marumoite used for?+

Marumoite is used in collector.

Find marumoite on the map

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