Rouaite is a very rare copper nitrate mineral typically found as small, dark green to bluish green tabular crystals or crusts. It is named after its type locality, the Roua copper mine in France, where it forms in oxidized zones of copper-rich ores.
Is this rouaite?
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 rouaite with a known reference. Rouaite sits at Mohs 3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: green.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: dark emerald green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: aggregates, equant grains, euhedral crystals.
Often confused with
Rouaite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Rouaite is noticeably harder (Mohs 3 vs. 2); streak differs, so Rouaite leaves green, Gerhardtite leaves pale green.
How to tell apart: Streak differs, so Rouaite leaves green, Malachite leaves pale green; luster reads vitreous on Rouaite and adamantine to vitreous; silky if fibrous; dull to earthy if massive on Malachite.
How to tell apart: Streak differs, so Rouaite leaves green, Connellite leaves pale greenish blue.
Often found alongside rouaite
Minerals reported to co-occur with rouaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu₂(NO₃)(OH)₃
- Mohs hardness
- 3
- Density
- 3.38 g/cm³
- Colors
- Dark emerald green
- Streak
- Green
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Aggregates, equant grains, euhedral crystals
- Cleavage
- Perfect on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Rare in cavities in cuprite from a hydrothermal copper deposit, the nitrate perhaps supplied from guano or organic matter in host-rock pelites (Roua mines, France)
Where rockhounds find rouaite
Classic worldwide localities
- Sterling Hill, Ogdensburg, Sussex Co., New Jersey, USA
- Roua copper mines, about 50 km north of Nice, Alpes Maritimes, France
Field-hunting tip
Where it forms: Rare in cavities in cuprite from a hydrothermal copper deposit, the nitrate perhaps supplied from guano or organic matter in host-rock pelites (Roua mines, France). If you start seeing cuprite, copper, silver in float, you are in the right ground. Typical habit: aggregates, equant grains, euhedral crystals. Train your eye for that shape before scanning the outcrop.
Common questions
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Find rouaite on the map
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