Feynmanite is a very rare uranyl sulfate mineral discovered in the oxidized zone of uranium mines. It typically forms small, vibrant yellow tabular crystals or crusts that are highly fluorescent under specific conditions and require careful handling due to radioactivity.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Feynmanite

Hardness: 2
Luster: Vitreous
Streak: White
Transparency: Transparent

No image

Is this feynmanite?

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 feynmanite with a known reference. Feynmanite 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. Feynmanite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Feynmanite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: yellow, yellowish-green.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: tabular crystals, crusts.

Often confused with

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

mineral

Johannite

Mohs 2

How to tell apart: Streak differs — Feynmanite leaves white, Johannite leaves pale green.

How to tell apart: Streak differs — Feynmanite leaves white, Zippeite leaves yellow; luster reads vitreous on Feynmanite and pearly on Zippeite.

Compare →

Often found alongside feynmanite

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

All properties

Chemical formula: Na₂UO₂(SO₄)₂·2H₂O
Mohs hardness: 2
Density: 2.81 g/cm³
Colors: Yellow Yellowish-green
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Tabular Crystals, Crusts
Cleavage: Perfect
Rarity: Rare
Uses: Collector
Host rock: Uranium-bearing Sedimentary Rocks
Typical price: $50-300 per specimen

Where rockhounds find feynmanite

Classic worldwide localities

Repete Mine, Utah, USA

Field-hunting tip

Look in uranium-bearing sedimentary rocks country — that is the host setting where feynmanite typically forms. If you start seeing johannite, zippeite, gypsum in float, you are in the right ground. Field specimens usually show a tabular crystals, crusts habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify feynmanite?+

Mohs hardness is 2. It typically shows a vitreous luster. The streak is white. Common colors include yellow, yellowish-green.

Where is feynmanite found?+

Notable localities include Repete Mine, Utah, USA.

How much is feynmanite worth?+

Typical asking prices fall in the range of $50-300 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

Is feynmanite safe to handle?+

This mineral is radioactive. It contains toxic constituents. Contains uranium, which is radioactive, and sulfate compounds. Store in a shielded container, avoid inhalation of dust, and wash hands thoroughly after handling. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like feynmanite?+

Feynmanite 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 feynmanite?+

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

What kind of rock does feynmanite form in?+

Feynmanite typically forms in uranium-bearing sedimentary rocks. Working float back to the host body is the standard way to chase a fresh occurrence.

What is feynmanite used for?+

Feynmanite is used in collector.

Find feynmanite on the map

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