Pseudocotunnite is a rare lead potassium chloride mineral typically formed by volcanic sublimation. It is most frequently encountered as yellow to colorless acicular or fibrous crystals forming crusts in active or dormant volcanic fumaroles.

Hardness

2-3

Mohs

Luster

Dull

Streak

White

Transparency

Semitransparent

mineralrare

Pseudocotunnite

Hardness: 2-3
Luster: Dull
Streak: White
Transparency: Semitransparent

Is this pseudocotunnite?

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 pseudocotunnite with a known reference. Pseudocotunnite sits at Mohs 2-3, 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: dull.
4
Match the color range
Compare against the expected color range: yellow, colorless, green yellow, white.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: acicular, aggregates, platy.

Often confused with

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

mineral

Cotunnite

Mohs 2.5

How to tell apart: Luster reads dull on Pseudocotunnite and adamantine, silky to pearly on Cotunnite.

How to tell apart: Luster reads dull on Pseudocotunnite and adamantine, pearly on {001} on Matlockite.

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Often found alongside pseudocotunnite

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

All properties

Chemical formula: K₂PbCl₄
Mohs hardness: 2-3
Density: 4.25 g/cm³
Colors: Yellow Colorless Green yellow White
Streak: White
Luster: Dull
Transparency: Semitransparent
Crystal system: Orthorhombic
Crystal habit: Acicular, aggregates, platy
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: In volcanic fumaroles

Where rockhounds find pseudocotunnite

Classic worldwide localities

Vesuvius, Campania, Italy

Field-hunting tip

Where it forms: In volcanic fumaroles. If you start seeing tenorite, cotunnite in float, you are in the right ground. Typical habit: acicular, aggregates, platy. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify pseudocotunnite?+

Mohs hardness is 2-3. Luster: dull. The streak is white. Common colors include yellow, colorless, green yellow, white.

Where is pseudocotunnite found?+

Notable localities include Vesuvius, Campania, Italy.

Is pseudocotunnite safe to handle?+

Pseudocotunnite contains lead. Contains lead, a toxic heavy metal. Wash hands thoroughly after handling and avoid ingestion or inhalation of dust.

What rocks look like pseudocotunnite?+

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

What minerals are found with pseudocotunnite?+

Pseudocotunnite commonly co-occurs with Tenorite, Cotunnite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does pseudocotunnite form in?+

Where it forms: In volcanic fumaroles. Working float back to the host body is the standard way to chase a fresh occurrence.

What is pseudocotunnite used for?+

Pseudocotunnite is used in collector.

Find pseudocotunnite on the map

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