Gerhardtite is a rare copper nitrate mineral typically found in arid regions as an oxidation product of copper deposits. It is recognized by its vibrant emerald-green color and thin, platy crystals that often form crusts or delicate clusters.
Is this gerhardtite?
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 gerhardtite with a known reference. Gerhardtite 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. Streak: pale green.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: green, dark green.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: tabular crystals, sometimes elongated or pseudo-hexagonal; also occurs in crusts or granular aggregates.
Often confused with
Gerhardtite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Malachite is the harder of the two (Mohs 3.5-4 vs. 2); luster reads vitreous on Gerhardtite and adamantine to vitreous; silky if fibrous; dull to earthy if massive on Malachite.
How to tell apart: Atacamite is the harder of the two (Mohs 3-3.5 vs. 2); streak differs, so Gerhardtite leaves pale green, Atacamite leaves apple-green; luster reads vitreous on Gerhardtite and adamantine to vitreous on Atacamite.
How to tell apart: Libethenite is the harder of the two (Mohs 4 vs. 2); streak differs, so Gerhardtite leaves pale green, Libethenite leaves light green.
Often found alongside gerhardtite
Minerals reported to co-occur with gerhardtite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu₂NO₃(OH)₃
- Mohs hardness
- 2
- Density
- 3.40-3.43 g/cm³
- Colors
- Streak
- Pale green
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Tabular crystals, sometimes elongated or pseudo-hexagonal; also occurs in crusts or granular aggregates
- Cleavage
- On {001}, perfect; on {100}, good
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare secondary mineral in oxidized portions of copper deposits
Where rockhounds find gerhardtite
Classic worldwide localities
- United Verde mine, Jerome, Yavapai Co., Arizona, USA
- Daisy shaft, Mineral Hill mine, Pima district, Pima Co., Arizona, USA
- Chase Creek Canyon, Greenlee Co., Arizona, USA
- Dzhezkazgan, Kazakhstan
- Ramsbeck, Westphalia, Germany
- Roua copper mines, about 50 km north of Nice, Alpes Maritimes, France
Field-hunting tip
Where it forms: A rare secondary mineral in oxidized portions of copper deposits. If you start seeing cuprite, malachite, atacamite in float, you are in the right ground. Typical habit: tabular crystals, sometimes elongated or pseudo-hexagonal; also occurs in crusts or granular aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
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Find gerhardtite on the map
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