Uranopilite is a secondary uranium sulfate mineral that typically forms as bright yellow, velvety efflorescences on uranium-bearing rocks. It is highly radioactive and recognizable by its intense, vibrant fluorescence under ultraviolet light.

Hardness

2.5

Mohs

Luster

Pearly

Streak

Pale Yellow

Transparency

Transparent

mineraluncommon

Uranopilite

Hardness: 2.5
Luster: Pearly
Streak: Pale Yellow
Transparency: Transparent

Is this uranopilite?

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 uranopilite with a known reference. Uranopilite 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. Uranopilite leaves a pale yellow streak.
3
Read the luster
Hold the specimen under a strong light. Uranopilite typically shows a pearly luster.
4
Match the color range
Compare against the expected color range: yellow, bright yellow, greenish-yellow.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: acicular or fibrous crusts, velvety coatings, spherical aggregates.

Often confused with

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

How to tell apart: Streak differs — Uranopilite leaves pale yellow, Zippeite leaves yellow.

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Often found alongside uranopilite

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

All properties

Chemical formula: (UO₂)₆(SO₄)O₂(OH)₆·14H₂O
Mohs hardness: 2.5
Density: 4.0 g/cm³
Colors: Yellow Bright Yellow Greenish-yellow
Streak: Pale Yellow
Luster: Pearly
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Acicular or Fibrous Crusts, Velvety Coatings, Spherical Aggregates
Cleavage: Perfect
Fluorescence: Bright Yellowish-green Under UV Light
Rarity: Uncommon
Uses: Collector
Host rock: Oxidized Uranium Ore Deposits
Typical price: $20-150 for small cabinet specimens

Where rockhounds find uranopilite

Classic worldwide localities

Jachymov, Czech Republic
Joachimsthal, Czech Republic
Happy Jack Mine, Utah, USA
Wheal Owles, Cornwall, UK

Field-hunting tip

Look in oxidized uranium ore deposits country — that is the host setting where uranopilite typically forms. If you start seeing zippeite, gypsum, johannite in float, you are in the right ground. Field specimens usually show a acicular or fibrous crusts, velvety coatings, spherical aggregates habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify uranopilite?+

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

Where is uranopilite found?+

Notable localities include Jachymov, Czech Republic; Joachimsthal, Czech Republic; Happy Jack Mine, Utah, USA; Wheal Owles, Cornwall, UK.

How much is uranopilite worth?+

Typical asking prices fall in the range of $20-150 for small cabinet specimens. Quality, size, and provenance can move individual specimens well outside that range.

Is uranopilite safe to handle?+

This mineral is radioactive. It contains toxic constituents. This mineral is highly radioactive and contains uranium. Handle with minimal contact, store in a lead-lined container, and wash hands thoroughly after handling. Avoid dust inhalation. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like uranopilite?+

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

What minerals are found with uranopilite?+

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

What kind of rock does uranopilite form in?+

Uranopilite typically forms in oxidized uranium ore deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is uranopilite used for?+

Uranopilite is used in collector.

Find uranopilite on the map

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