Mathesiusite is a rare secondary uranium sulfate mineral discovered in the historic mining district of Jáchymov. It typically forms thin, bright yellow platy crystals coating other uranium minerals in oxidized hydrothermal zones. Due to its radioactive nature and extreme rarity, it is highly sought after by advanced systematic mineral collectors.

Hardness

2.5

Mohs

Luster

Vitreous

Streak

Yellow

Transparency

Transparent

mineralrare

Mathesiusite

Hardness: 2.5
Luster: Vitreous
Streak: Yellow
Transparency: Transparent

Is this mathesiusite?

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 mathesiusite with a known reference. Mathesiusite sits at Mohs 2.5 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Mathesiusite leaves a yellow streak.
3
Read the luster
Hold the specimen under a strong light. Mathesiusite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: yellow, greenish-yellow.
5
Look at form & habit
Crystal system: tetragonal. Typical habit: platy crystals.

Often confused with

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

mineral

Johannite

Mohs 2

How to tell apart: Streak differs — Mathesiusite leaves yellow, Johannite leaves pale green.

How to tell apart: Luster reads vitreous on Mathesiusite and pearly on Zippeite.

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Often found alongside mathesiusite

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

All properties

Chemical formula: K₅(UO₂)₄(SO₄)₄(OH)₃·3H₂O
Mohs hardness: 2.5
Density: 4.15 g/cm³
Colors: Yellow Greenish-yellow
Streak: Yellow
Luster: Vitreous
Transparency: Transparent
Crystal system: Tetragonal
Crystal habit: Platy Crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Hydrothermal Veins
Typical price: $100-500 thumbnail

Where rockhounds find mathesiusite

Classic worldwide localities

Jáchymov, Czech Republic

Field-hunting tip

Look in hydrothermal veins country — that is the host setting where mathesiusite typically forms. If you start seeing uraninite, johannite, arsenopyrite in float, you are in the right ground. Field specimens usually show a platy crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify mathesiusite?+

Mohs hardness is 2.5. It typically shows a vitreous luster. The streak is yellow. Common colors include yellow, greenish-yellow.

Where is mathesiusite found?+

Notable localities include Jáchymov, Czech Republic.

How much is mathesiusite worth?+

Typical asking prices fall in the range of $100-500 thumbnail. Quality, size, and provenance can move individual specimens well outside that range.

Is mathesiusite safe to handle?+

This mineral is radioactive. It contains toxic constituents. This mineral contains uranium and is radioactive. Handle with care using proper safety protocols, store in a lead-lined container, and wash hands thoroughly after handling. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like mathesiusite?+

Mathesiusite 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 mathesiusite?+

Mathesiusite commonly co-occurs with Uraninite, Johannite, Arsenopyrite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does mathesiusite form in?+

Mathesiusite typically forms in hydrothermal veins. Working float back to the host body is the standard way to chase a fresh occurrence.

What is mathesiusite used for?+

Mathesiusite is used in collector.

Find mathesiusite on the map

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