Pseudojohannite is a rare secondary uranium sulfate mineral typically found as small, moss-green tabular crystals in oxidized uranium deposits. It is frequently associated with johannite, from which it can be distinguished by specific optical properties and its triclinic structure. Collectors should treat it with caution due to its high radioactivity and solubility.

Hardness

2-3

Mohs

Transparency

Transparent to translucent

mineralrare

Pseudojohannite

Hardness: 2-3
Transparency: Transparent to translucent

No image

Is this pseudojohannite?

3-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 pseudojohannite with a known reference. Pseudojohannite sits at Mohs 2-3, softer than the next harder reference, harder than the previous one.
2
Match the color range
Compare against the expected color range: moss green, olive gray.
3
Look at form & habit
Crystal system: triclinic. Typical habit: prismatic, tabular.

Often confused with

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

Often found alongside pseudojohannite

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

All properties

Chemical formula: Cu₃(UO₂)₄O₄(SO₄)₂(OH)₂·12H₂O
Mohs hardness: 2-3
Density: 4.31 g/cm³
Colors: Moss greenOlive gray
Transparency: Transparent to translucent
Crystal system: Triclinic
Crystal habit: Prismatic, tabular
Cleavage: Perfect on {1̄01}
Fluorescence: Bright yellow-green under UV
Rarity: Rare
Uses: Collector
Host rock: A secondary mineral formed by the interaction of acidic sulfate mine water with uraninite or uranyl silicate minerals

Where rockhounds find pseudojohannite

Classic worldwide localities

Widowmaker mine, White Canyon, San Juan County, Utah, USA
Rovnost (Werner) shaft, Jáchymov (St. Joachimsthal), Western Bohemia, Czech Republic
Musonoï quarry, Katanga, Democratic Republic of the Congo
La Creusaz prospect, canton Valais, Western Swiss Alps, Switzerland

Field-hunting tip

Where it forms: A secondary mineral formed by the interaction of acidic sulfate mine water with uraninite or uranyl silicate minerals. If you start seeing johannite, uranopilite, gypsum in float, you are in the right ground. Typical habit: prismatic, tabular. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify pseudojohannite?+

Mohs hardness is 2-3. Common colors include moss green, olive gray.

Where is pseudojohannite found?+

Notable localities include Widowmaker mine, White Canyon, San Juan County, Utah, USA; Rovnost (Werner) shaft, Jáchymov (St. Joachimsthal), Western Bohemia, Czech Republic; Musonoï quarry, Katanga, Democratic Republic of the Congo; La Creusaz prospect, canton Valais, Western Swiss Alps, Switzerland.

Is pseudojohannite safe to handle?+

Pseudojohannite contains copper and uranium or thorium and calls for real care. Radioactive material; keep shielded, store in sealed containers, and wash hands thoroughly after handling. Avoid dust inhalation.

What rocks look like pseudojohannite?+

Pseudojohannite is most often confused with Johannite, Meta-autunite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with pseudojohannite?+

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

What kind of rock does pseudojohannite form in?+

Where it forms: A secondary mineral formed by the interaction of acidic sulfate mine water with uraninite or uranyl silicate minerals. Working float back to the host body is the standard way to chase a fresh occurrence.

What is pseudojohannite used for?+

Pseudojohannite is used in collector.

Find pseudojohannite on the map

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