Asselbornite is a extremely rare secondary uranium mineral that appears as tiny yellow crystals. It is best known for its type locality in Asselborn, Luxembourg, where it forms in oxidized hydrothermal veins. Because of its scarcity and composition, it is highly sought after by advanced radioactive mineral collectors.

Hardness

Mohs

Luster

Greasy to adamantine

Streak

Lemon

Transparency

Translucent

mineralrare

Asselbornite

Hardness: 3
Luster: Greasy to adamantine
Streak: Lemon
Transparency: Translucent

Is this asselbornite?

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 asselbornite with a known reference. Asselbornite sits at Mohs 3, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: lemon.
3
Read the luster
Hold the specimen under a strong light. Luster: greasy to adamantine.
4
Match the color range
Compare against the expected color range: brown, lemon yellow.
5
Look at form & habit
Crystal system: cubic. Typical habit: euhedral crystals.

Often confused with

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

mineral

Uraninite

Mohs 5-6

How to tell apart: Uraninite is the harder of the two (Mohs 5-6 vs. 3); streak differs, so Asselbornite leaves lemon, Uraninite leaves brownish black, gray, olive-green, shining; luster reads greasy to adamantine on Asselbornite and submetallic to greasy, dull on Uraninite.

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Often found alongside asselbornite

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

All properties

Chemical formula: Pb(UO₂)₄(BiO)₃(AsO₄)₂(OH)₇·4H₂O
Mohs hardness: 3
Density: 5.6 g/cm³
Colors: Brown Lemon yellow
Streak: Lemon
Luster: Greasy to adamantine
Transparency: Translucent
Crystal system: Cubic
Crystal habit: Euhedral crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: On a museum specimen initially, later at the locality

Where rockhounds find asselbornite

Classic worldwide localities

Walpurgis vein, Weisser Hirsch mine, Neustädtel-Schneeberg, Saxony, Germany

Field-hunting tip

Where it forms: On a museum specimen initially, later at the locality. If you start seeing uranospinite, uranophane, uranosphaerite in float, you are in the right ground. Typical habit: euhedral crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify asselbornite?+

Mohs hardness is 3. Luster: greasy to adamantine. The streak is lemon. Common colors include brown, lemon yellow.

Where is asselbornite found?+

Notable localities include Walpurgis vein, Weisser Hirsch mine, Neustädtel-Schneeberg, Saxony, Germany.

Is asselbornite safe to handle?+

Asselbornite contains arsenic, lead and uranium or thorium and calls for real care. This mineral is both radioactive and contains lead and arsenic. Handle with gloves, store in a sealed container, and wash hands thoroughly after contact.

What rocks look like asselbornite?+

Asselbornite is most often confused with Uraninite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with asselbornite?+

Asselbornite commonly co-occurs with Uranospinite, Uranophane, Uranosphaerite, Quartz. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does asselbornite form in?+

Where it forms: On a museum specimen initially, later at the locality. Working float back to the host body is the standard way to chase a fresh occurrence.

What is asselbornite used for?+

Asselbornite is used in collector.

Find asselbornite on the map

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