Johannite is a rare copper-uranium sulfate typically found as vibrant emerald-green crusts or thin, bladed crystals. It forms in the oxidized zones of uranium deposits and is highly sought after by collectors for its brilliant fluorescence and intense color.

Hardness

2-2.5

Mohs

Luster

Vitreous

Streak

Pale green

Transparency

Transparent to translucent

mineralrare

Johannite

Hardness: 2-2.5
Luster: Vitreous
Streak: Pale green
Transparency: Transparent to translucent

Is this johannite?

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 johannite with a known reference. Johannite sits at Mohs 2-2.5, 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.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: yellow, greenish yellow.
5
Look at form & habit
Crystal system: triclinic. Typical habit: druse, massive, reniform.

Often confused with

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

mineral

Chalcanthite

Mohs 2.5

How to tell apart: Streak differs, so Johannite leaves pale green, Chalcanthite leaves white.

How to tell apart: Brochantite is the harder of the two (Mohs 3.5-4 vs. 2-2.5).

Compare →

Often found alongside johannite

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

All properties

Chemical formula: Cu(UO₂)₂(SO₄)₂(OH)₂·8H₂O
Mohs hardness: 2-2.5
Density: 3.32 g/cm³
Colors: Yellow Greenish yellow
Streak: Pale green
Luster: Vitreous
Transparency: Transparent to translucent
Crystal system: Triclinic
Crystal habit: Druse, massive, reniform
Cleavage: On {100}, good
Rarity: Rare
Uses: Collector
Host rock: A rare secondary mineral in the oxidized portions of sulfide-bearing uraninite deposits, commonly of post-mine formation

Where rockhounds find johannite

Classic worldwide localities

Kirk, Wood, and other mines, Central City, Gilpin Co., in the Schwartzwalder mine, near Golden, Jefferson Co., Colorado, USA
Utah, at the Oyler mine, Henry Mountains district, the Frey No. 4 mine, and the Happy Jack mine, White Canyon district, San Juan Co., and at Marysvale, Ohio district, Piute Co., USA
Hillside mine, about 5.5 km north of Bagdad, Yavapai Co., Arizona, USA
Ram claims, Pinto Mountains, Riverside Co., California, USA
Eliáš mine, Jáchymov (Joachimsthal), Czech Republic
Johanngeorgenstadt, Saxony, and Wölsendorf, Bavaria, Germany

Field-hunting tip

Where it forms: A rare secondary mineral in the oxidized portions of sulfide-bearing uraninite deposits, commonly of post-mine formation. If you start seeing gypsum, zippeite, uranopilite in float, you are in the right ground. Typical habit: druse, massive, reniform. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify johannite?+

Mohs hardness is 2-2.5. Luster: vitreous. The streak is pale green. Common colors include yellow, greenish yellow.

Where is johannite found?+

Notable localities include Kirk, Wood, and other mines, Central City, Gilpin Co., in the Schwartzwalder mine, near Golden, Jefferson Co., Colorado, USA; Utah, at the Oyler mine, Henry Mountains district, the Frey No. 4 mine, and the Happy Jack mine, White Canyon district, San Juan Co., and at Marysvale, Ohio district, Piute Co., USA; Hillside mine, about 5.5 km north of Bagdad, Yavapai Co., Arizona, USA; Ram claims, Pinto Mountains, Riverside Co., California, USA; Eliáš mine, Jáchymov (Joachimsthal), Czech Republic.

Is johannite safe to handle?+

Johannite contains copper and uranium or thorium and calls for real care. Radioactive mineral; handle with gloves, avoid inhalation of dust, wash hands thoroughly after contact, and store in a lead-lined container.

What rocks look like johannite?+

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

What minerals are found with johannite?+

Johannite commonly co-occurs with Gypsum, Zippeite, Uranopilite, Brochantite, Chalcanthite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does johannite form in?+

Where it forms: A rare secondary mineral in the oxidized portions of sulfide-bearing uraninite deposits, commonly of post-mine formation. Working float back to the host body is the standard way to chase a fresh occurrence.

What is johannite used for?+

Johannite is used in collector.

Find johannite on the map

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