Plavnoite is a rare secondary uranium sulfate mineral typically found as a reddish to reddish orange crust or powdery coating on weathered uranium-bearing ores. It is primarily known from the Jáchymov region and is of interest primarily to advanced mineral collectors focusing on uranium species.

Hardness

Mohs

Luster

Vitreous to silky

Streak

Pale orange

Transparency

Transparent

mineralrareJohannite Group family

Plavnoite

Hardness: ~2
Luster: Vitreous to silky
Streak: Pale orange
Transparency: Transparent

Is this plavnoite?

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 plavnoite with a known reference. Plavnoite sits at Mohs ~2, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: pale orange.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous to silky.
4
Match the color range
Compare against the expected color range: reddish, reddish orange.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: microcrystalline crusts, earthy aggregates.

Often confused with

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

How to tell apart: Streak differs, so Plavnoite leaves pale orange, Zippeite leaves yellow white.

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Often found alongside plavnoite

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

All properties

Chemical formula: K₀.₈Mn₀.₆[(UO₂)₂O₂(SO₄)]·3.5H₂O
Mohs hardness: ~2
Density: 4.926 g/cm³
Colors: Reddish Reddish orange
Streak: Pale orange
Luster: Vitreous to silky
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Microcrystalline crusts, earthy aggregates
Cleavage: Perfect on {010}
Rarity: Rare
Uses: Collector, Scientific research
Host rock: A secondary alteration mineral formed by hydration-oxidation weathering of uraninite in a hydrothermal Ag-Bi-Co-Ni-U vein deposit

Where rockhounds find plavnoite

Classic worldwide localities

Jáchymov, Czech Republic
Plavno, Czech Republic

Field-hunting tip

Where it forms: A secondary alteration mineral formed by hydration-oxidation weathering of uraninite in a hydrothermal Ag-Bi-Co-Ni-U vein deposit. If you start seeing marécottite, magnesiozippeite, blatonite in float, you are in the right ground. Typical habit: microcrystalline crusts, earthy aggregates. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify plavnoite?+

Mohs hardness is ~2. Luster: vitreous to silky. The streak is pale orange. Common colors include reddish, reddish orange.

Where is plavnoite found?+

Notable localities include Jáchymov, Czech Republic; Plavno, Czech Republic.

Is plavnoite safe to handle?+

Plavnoite contains uranium or thorium and calls for real care. This mineral is radioactive due to its uranium content and should be handled with standard radiological precautions. Keep in a sealed container, wash hands after handling, and avoid creating dust.

What rocks look like plavnoite?+

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

What minerals are found with plavnoite?+

Plavnoite commonly co-occurs with Marécottite, Magnesiozippeite, Blatonite, Gypsum. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does plavnoite form in?+

Where it forms: A secondary alteration mineral formed by hydration-oxidation weathering of uraninite in a hydrothermal Ag-Bi-Co-Ni-U vein deposit. Working float back to the host body is the standard way to chase a fresh occurrence.

What is plavnoite used for?+

Plavnoite is used in collector, scientific research.

Find plavnoite on the map

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