Ammoniomathesiusite is a rare uranyl sulfate mineral belonging to the mathesiusite group. It typically appears as small, vivid yellow tabular crystals in oxidized uranium-bearing hydrothermal deposits, most notably in Jáchymov. Due to its extreme rarity and radioactivity, it is almost exclusively sought after by advanced mineral collectors specializing in uranium minerals.

Hardness

2-3

Mohs

Luster

Vitreous

Streak

Pale Yellow

Transparency

Transparent

mineralrareMathesiusite Group family

Ammoniomathesiusite

Hardness: 2-3
Luster: Vitreous
Streak: Pale Yellow
Transparency: Transparent

No image

Is this ammoniomathesiusite?

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 ammoniomathesiusite with a known reference. Ammoniomathesiusite 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. Ammoniomathesiusite leaves a pale yellow streak.
3
Read the luster
Hold the specimen under a strong light. Ammoniomathesiusite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: yellow.
5
Look at form & habit
Crystal system: tetragonal. Typical habit: tabular crystals.

Often confused with

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

mineral

Mathesiusite

Mohs 2.5

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

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

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Often found alongside ammoniomathesiusite

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

All properties

Chemical formula: (NH₄)₅(UO₂₄)(SO₄)₄(OH)₄·4H₂O
Mohs hardness: 2-3
Density: 3.84 g/cm³
Colors: Yellow
Streak: Pale Yellow
Luster: Vitreous
Transparency: Transparent
Crystal system: Tetragonal
Crystal habit: Tabular Crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Hydrothermal Uranium Veins
Typical price: $100-500 per micro-mount

Where rockhounds find ammoniomathesiusite

Classic worldwide localities

Jáchymov, Czech Republic

Field-hunting tip

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

Common questions

How do you identify ammoniomathesiusite?+

Mohs hardness is 2-3. It typically shows a vitreous luster. The streak is pale yellow. Common colors include yellow.

Where is ammoniomathesiusite found?+

Notable localities include Jáchymov, Czech Republic.

How much is ammoniomathesiusite worth?+

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

Is ammoniomathesiusite safe to handle?+

This mineral is radioactive. It contains toxic constituents. Contains uranium; handle with care, avoid inhalation of dust, wash hands thoroughly after handling, and store in a lead-lined or secure container. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like ammoniomathesiusite?+

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

What minerals are found with ammoniomathesiusite?+

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

What kind of rock does ammoniomathesiusite form in?+

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

What is ammoniomathesiusite used for?+

Ammoniomathesiusite is used in collector.

Find ammoniomathesiusite on the map

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