Geigerite is a very rare manganese arsenate mineral typically found as small, pearly, platy crystals. It is primarily known from the historic manganese mines of Langban, Sweden, often occurring in association with other rare manganese species.

Hardness

Mohs

Luster

Vitreous to pearly

Streak

White

Transparency

Transparent to translucent

mineralrare

Geigerite

Hardness: ~3
Luster: Vitreous to pearly
Streak: White
Transparency: Transparent to translucent

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Is this geigerite?

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 geigerite with a known reference. Geigerite 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. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous to pearly.
4
Match the color range
Compare against the expected color range: colorless, red.
5
Look at form & habit
Crystal system: triclinic. Typical habit: platy crystals.

Often confused with

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

Often found alongside geigerite

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

All properties

Chemical formula: Mn₅(AsO₄)₂(AsO₃OH)₂·10H₂O
Mohs hardness: ~3
Density: 3.05 g/cm³
Colors: Colorless Red
Streak: White
Luster: Vitreous to pearly
Transparency: Transparent to translucent
Crystal system: Triclinic
Crystal habit: Platy crystals
Cleavage: Perfect on {010}
Rarity: Rare
Uses: Collector
Host rock: In cavities in radiolarites, formed by metamorphism of manganese oxide ores

Where rockhounds find geigerite

Classic worldwide localities

Falotta mine, Oberhalbstein, Graubünden, Switzerland

Field-hunting tip

Where it forms: In cavities in radiolarites, formed by metamorphism of manganese oxide ores. If you start seeing brandtite, sarkinite, grischunite in float, you are in the right ground. Typical habit: platy crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify geigerite?+

Mohs hardness is ~3. Luster: vitreous to pearly. The streak is white. Common colors include colorless, red.

Where is geigerite found?+

Notable localities include Falotta mine, Oberhalbstein, Graubünden, Switzerland.

Is geigerite safe to handle?+

Geigerite contains arsenic and calls for real care. Contains arsenic, which is toxic if ingested or inhaled as dust. Handle with care and wash hands thoroughly after handling.

What rocks look like geigerite?+

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

What minerals are found with geigerite?+

Geigerite commonly co-occurs with Brandtite, Sarkinite, Grischunite, Bergslagite, Manganberzeliite, Tilasite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does geigerite form in?+

Where it forms: In cavities in radiolarites, formed by metamorphism of manganese oxide ores. Working float back to the host body is the standard way to chase a fresh occurrence.

What is geigerite used for?+

Geigerite is used in collector.

Find geigerite on the map

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