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.
Is this johannite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch johannite with a known reference. Johannite sits at Mohs 2 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Johannite leaves a pale green streak.
- 3Read the lusterHold the specimen under a strong light. Johannite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: emerald-green, apple-green, yellowish-green.
- 5Look at form & habitCrystal system: triclinic. Typical habit: bladed, lath-like, or acicular crystals often in radial aggregates or crusts.
Often confused with
Johannite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Johannite leaves pale green, Chalcanthite leaves white.
How to tell apart: Streak differs — Johannite leaves pale green, Autunite leaves pale yellow; luster reads vitreous on Johannite and pearly on Autunite.
How to tell apart: Brochantite is the harder of the two (Mohs 3.5-4 vs. 2); streak differs — Johannite leaves pale green, Brochantite leaves pale-green.
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
- Density
- 3.32 g/cm³
- Streak
- Pale Green
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Triclinic
- Crystal habit
- Bladed, Lath-like, Or Acicular Crystals Often in Radial Aggregates or Crusts
- Cleavage
- Perfect On {010}
- Fluorescence
- Bright Yellowish-green Under SW and LW UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Zones of Uranium-bearing Hydrothermal Deposits
- Typical price
- $50-500 thumbnail depending on crystal size and quality
Where rockhounds find johannite
Classic worldwide localities
- Jachymov, Czech Republic
- Temple Mountain, Utah, USA
- Musonoi Mine, DR Congo
- Wolsendorf, Germany
Field-hunting tip
Look in oxidized zones of uranium-bearing hydrothermal deposits country — that is the host setting where johannite typically forms. If you start seeing uraninite, zippeite, gypsum in float, you are in the right ground. Field specimens usually show a bladed, lath-like, or acicular crystals often in radial aggregates or crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find johannite on the map
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