Gilmarite is a rare copper arsenate mineral typically found as small, bright green acicular crystals or delicate radiating sprays. It is primarily identified by its occurrence in highly oxidized copper-arsenic zones, most notably at the Cap Garonne mine in France.
Is this gilmarite?
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 gilmarite with a known reference. Gilmarite 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: blue-green.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: greenish blue.
- 5Look at form & habitCrystal system: triclinic. Typical habit: acicular crystals, radial aggregates.
Often confused with
Gilmarite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Gilmarite leaves blue-green, Clinoclase leaves bluish green.
How to tell apart: Cornwallite is the harder of the two (Mohs 4.5 vs. ~3); streak differs, so Gilmarite leaves blue-green, Cornwallite leaves pale green.
Often found alongside gilmarite
Minerals reported to co-occur with gilmarite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu₃(AsO₄)(OH)₃
- Mohs hardness
- ~3
- Density
- 4.2 g/cm³
- Colors
- Streak
- Blue-green
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Triclinic
- Crystal habit
- Acicular crystals, radial aggregates
- Cleavage
- Good on {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare secondary mineral associated with other copper arsenates and copper arsenides in the oxidized zone
Where rockhounds find gilmarite
Classic worldwide localities
- Roua copper mines, about 50 km north of Nice, Alpes Maritimes, France
Field-hunting tip
Where it forms: A rare secondary mineral associated with other copper arsenates and copper arsenides in the oxidized zone. If you start seeing cuprite, posnjakite, langite in float, you are in the right ground. Typical habit: acicular crystals, radial aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify gilmarite?+
Where is gilmarite found?+
Is gilmarite safe to handle?+
What rocks look like gilmarite?+
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Find gilmarite on the map
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