Ottohahnite is a rare secondary sodium uranyl sulfate that typically forms as a dehydration product of higher-hydrate uranium minerals. Collectors generally find it as small, yellowish platy crystals or crusts associated with other uranium secondary species in oxidized zones of ore deposits.

Hardness

~2.5

Mohs

Luster

Vitreous

Streak

Pale green-yellow

Transparency

Transparent

mineralrare

Ottohahnite

Hardness: ~2.5
Luster: Vitreous
Streak: Pale green-yellow
Transparency: Transparent

Is this ottohahnite?

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 ottohahnite with a known reference. Ottohahnite 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. Streak: pale green-yellow.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: greenish yellow.
5
Look at form & habit
Crystal system: triclinic. Typical habit: platy crystals, crusts, aggregates.

Often confused with

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

Often found alongside ottohahnite

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

All properties

Chemical formula: Na₆(UO₂)₂(SO₄)₅(H₂O)₇·1.5H₂O
Mohs hardness: ~2.5
Density: 2.973 g/cm³
Colors: Greenish yellow
Streak: Pale green-yellow
Luster: Vitreous
Transparency: Transparent
Crystal system: Triclinic
Crystal habit: Platy crystals, crusts, aggregates
Cleavage: None
Fluorescence: Bright bluish green fluorescence under SW & LW UV
Rarity: Rare
Uses: Collector
Host rock: As efflorescent crusts on mine walls, formed by hydration-oxidation weathering of primary uranium minerals (mainly uraninite) by acidic solutions from the decomposition of sulfides

Where rockhounds find ottohahnite

Classic worldwide localities

Blue Lizard mine, Red Canyon, White Canyon district, San Juan County, Utah, USA

Field-hunting tip

Where it forms: As efflorescent crusts on mine walls, formed by hydration-oxidation weathering of primary uranium minerals (mainly uraninite) by acidic solutions from the decomposition of sulfides. If you start seeing tamarugite, blödite, bluelizardite in float, you are in the right ground. Typical habit: platy crystals, crusts, aggregates. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify ottohahnite?+

Mohs hardness is ~2.5. Luster: vitreous. The streak is pale green-yellow. Common colors include greenish yellow.

Where is ottohahnite found?+

Notable localities include Blue Lizard mine, Red Canyon, White Canyon district, San Juan County, Utah, USA.

Is ottohahnite safe to handle?+

Ottohahnite contains uranium or thorium and calls for real care. Contains uranium and is radioactive; handle with care using gloves, avoid inhalation of dust, and store in a shielded container away from living areas.

What rocks look like ottohahnite?+

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

What minerals are found with ottohahnite?+

Ottohahnite commonly co-occurs with Tamarugite, Blödite, Bluelizardite, Bobcookite, Epsomite, Gypsum. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does ottohahnite form in?+

Where it forms: As efflorescent crusts on mine walls, formed by hydration-oxidation weathering of primary uranium minerals (mainly uraninite) by acidic solutions from the decomposition of sulfides. Working float back to the host body is the standard way to chase a fresh occurrence.

What is ottohahnite used for?+

Ottohahnite is used in collector.

Find ottohahnite on the map

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