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, so Uranopilite leaves pale yellow, Zippeite leaves yellow.

Compare →

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, 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.