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

Transparency

Opaque

mineralrareSartorite Group family

Marumoite

Hardness: 3
Luster: Metallic
Transparency: Opaque

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Is this marumoite?

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 marumoite with a known reference. Marumoite sits at Mohs 3, 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: lead gray.
4
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.

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: Pb₈As₁₀S₂₃
Mohs hardness: 3
Colors: Lead gray
Luster: Metallic
Transparency: Opaque
Crystal system: Monoclinic
Crystal habit: Prismatic crystals, striated
Rarity: Rare
Uses: Collector
Host rock: In a high-sulfidation, epithermal, Cu-Pb-Zn disseminated, massive sulfide deposit (Japan)

Where rockhounds find marumoite

Classic worldwide localities

Lengenbach quarry, Binntal, Vallis, Switzerland (type locality) and the Okoppe mine, Ohma Town, Shimokita-gun, Aomori Prefecture, northern Japan

Field-hunting tip

Where it forms: In a high-sulfidation, epithermal, Cu-Pb-Zn disseminated, massive sulfide deposit (Japan). If you start seeing sartorite, baumhauerite, pyrite in float, you are in the right ground. Typical habit: prismatic crystals, striated. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify marumoite?+

Mohs hardness is 3. Luster: metallic. Common colors include lead gray.

Where is marumoite found?+

Notable localities include Lengenbach quarry, Binntal, Vallis, Switzerland (type locality) and the Okoppe mine, Ohma Town, Shimokita-gun, Aomori Prefecture, northern Japan.

Is marumoite safe to handle?+

Marumoite contains arsenic and lead and calls for real care. Contains lead and arsenic; avoid inhalation of dust and wash hands thoroughly after handling.

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?+

Where it forms: In a high-sulfidation, epithermal, Cu-Pb-Zn disseminated, massive sulfide deposit (Japan). 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.