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

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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. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
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 2-2.5

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

How to tell apart: Streak differs, so Feynmanite leaves white, Zippeite leaves yellow white.

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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: Na(UO₂)(SO₄)(OH)·3.5H₂O
Mohs hardness: 2
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

Where rockhounds find feynmanite

Classic worldwide localities

Repete Mine, Utah, USA

Field-hunting tip

Where it forms: uranium-bearing sedimentary rocks. If you start seeing johannite, zippeite, gypsum in float, you are in the right ground. Typical habit: tabular crystals, crusts. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify feynmanite?+

Mohs hardness is 2. Luster: vitreous. The streak is white. Common colors include yellow, yellowish-green.

Where is feynmanite found?+

Notable localities include Repete Mine, Utah, USA.

Is feynmanite safe to handle?+

Feynmanite contains uranium or thorium and calls for real care. Contains uranium, which is radioactive, and sulfate compounds. Store in a shielded container, avoid inhalation of dust, and wash hands thoroughly after handling.

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?+

Where it forms: 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.