Oursinite is a very rare secondary uranium mineral that typically forms as delicate, needle-like yellow crystals or radial sprays. It is almost exclusively found in association with other rare uranyl minerals in oxidized deposits, making it a highly sought-after but difficult-to-acquire species for radioactive mineral collectors.

Hardness

2-3

Mohs

Luster

Vitreous

Streak

Yellow

Transparency

Transparent

mineralrareUranyl silicate family

Oursinite

Hardness: 2-3
Luster: Vitreous
Streak: Yellow
Transparency: Transparent

Is this oursinite?

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 oursinite with a known reference. Oursinite sits at Mohs 2-3, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Oursinite leaves a yellow streak.
3
Read the luster
Hold the specimen under a strong light. Oursinite 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: orthorhombic. Typical habit: acicular or fibrous radial aggregates.

Often confused with

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

mineral

Kasolite

Mohs 4-5

How to tell apart: Kasolite is the harder of the two (Mohs 4-5 vs. 2-3); luster reads vitreous on Oursinite and greasy on Kasolite.

How to tell apart: Luster reads vitreous on Oursinite and pearly on Boltwoodite.

Compare →

Often found alongside oursinite

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

All properties

Chemical formula: Co(UO₂)₂(SiO₃OH)₂·6H₂O
Mohs hardness: 2-3
Density: 3.8 g/cm³
Colors: Yellow Yellowish-green
Streak: Yellow
Luster: Vitreous
Transparency: Transparent
Crystal system: Orthorhombic
Crystal habit: Acicular or Fibrous Radial Aggregates
Cleavage: None
Fluorescence: Yellow-green Under UV
Rarity: Rare
Uses: Collector
Host rock: Oxidized Zones of Uranium Deposits
Typical price: $50-500 depending on specimen quality

Where rockhounds find oursinite

Classic worldwide localities

Shinkolobwe Mine, DR Congo

Field-hunting tip

Look in oxidized zones of uranium deposits country, the host setting where oursinite typically forms. If you start seeing sklodowskite, curite, vandenbrandeite in float, you are in the right ground. Field specimens usually show a acicular or fibrous radial aggregates habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify oursinite?+

Mohs hardness is 2-3. It typically shows a vitreous luster. The streak is yellow. Common colors include yellow, yellowish-green.

Where is oursinite found?+

Notable localities include Shinkolobwe Mine, DR Congo.

How much is oursinite worth?+

Typical asking prices fall in the range of $50-500 depending on specimen quality. Quality, size, and provenance can move individual specimens well outside that range.

Is oursinite safe to handle?+

This mineral is radioactive. It contains toxic constituents. This mineral contains uranium and cobalt. It is radioactive and toxic; handle with gloves, wash hands thoroughly after contact, and store in a lead-shielded or isolated container away from living areas. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like oursinite?+

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

What minerals are found with oursinite?+

Oursinite commonly co-occurs with Sklodowskite, Curite, Vandenbrandeite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does oursinite form in?+

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

What is oursinite used for?+

Oursinite is used in collector.

Find oursinite on the map

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