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, so 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, 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.