Atacamite
Atacamite is halide (copper hydroxychloride), Cu₂Cl(OH)₃. In the hand, it rates 3 to 3.5 on the Mohs scale, and it runs deep emerald green and blackish green. Brilliant deep-green slender prisms with an apple-green streak, born of copper meeting salty desert air. Hyper-arid oxidized copper deposits; classic: Atacama Desert (Chile, namesake), South Australia, Arizona (USA).
The geology.
Atacamite carries the formula Cu₂Cl(OH)₃. It belongs to the orthorhombic system. Its listing category is halide (copper hydroxychloride).
It sits at 3 to 3.5 on the Mohs scale. The surface reads adamantine to vitreous. Light behaviour is transparent to translucent. Specific gravity runs 3.75 to 3.77. The streak is apple green. It breaks with perfect cleavage; brittle.
Brilliant deep-green slender prisms with an apple-green streak, born of copper meeting salty desert air.
It turns up mostly as slender striated prisms, radiating sprays or crusts on matrix.
The origins.
Hyper-arid oxidized copper deposits; classic: Atacama Desert (Chile, namesake), South Australia, Arizona (USA).
On value, the database notes: collector mineral; rich Chilean sprays are mid-range.
Traditional associations.
In energy work traditions, associated with confidence and heart-forward communication.
This is lore, and we label it as lore. The measurable facts are further up the page.
Spotting the real thing.
Brilliant deep-green slender prisms with an apple-green streak, born of copper meeting salty desert air.
| Looks like | How to tell them apart |
|---|---|
| Malachite | Malachite fizzes in vinegar and forms banded rounded masses; atacamite doesn't fizz and forms prisms |
| Brochantite | Near-twin copper sulfate, lab tests often needed; brochantite is the commoner crust in non-chloride deposits |
| Dioptase | Dioptase is glassier, bluer-green, in stubby rhombohedra |
At-home tests.
A loupe and a window seat settle most questions about atacamite. No workshop required.
| Test | What you should see |
|---|---|
| By eye | Apple-green streak |
| Acid check | No fizz with vinegar |
| Scratch check | Knife scratches it easily |
If these checks leave you unsure, that is what appraisers are for. Do not file, heat or soak a piece to find out.
Care & handling.
At 3 to 3.5 on the Mohs scale this is a soft material. Keep it as a display piece, store it apart from harder stones, and skip daily-wear settings.
It breaks with perfect cleavage; brittle, which is worth knowing before you set it or drop it.
Most damage happens during cleaning, not wearing. Avoid steamers, ultrasonic tanks and anything from under the sink.
Copper mineral, wash hands after handling crumbly specimens.
A deeper look.
Extended detail on composition, sourcing, authentication and market value.
The physical record
The formula on record is Cu₂Cl(OH)₃. Crystal system: Orthorhombic. Specific gravity: 3.75 to 3.77. Streak: Apple green. Cleavage and fracture: Perfect cleavage; brittle.
How it reaches the market
Hyper-arid oxidized copper deposits; classic: Atacama Desert (Chile, namesake), South Australia, Arizona (USA).
What it gets confused with
Malachite: Malachite fizzes in vinegar and forms banded rounded masses; atacamite doesn't fizz and forms prisms. Brochantite: Near-twin copper sulfate, lab tests often needed; brochantite is the commoner crust in non-chloride deposits. Dioptase: Dioptase is glassier, bluer-green, in stubby rhombohedra.
What it is worth
Collector mineral; rich Chilean sprays are mid-range.
One more thing
Atacamite needs desert salt to form, it even turns up in the corrosion on bronze shipwrecks and sculptures.
An education-first guide.
There is nothing to buy on this page. Atacamite is not part of our catalogue, and the guide is here anyway because somebody searching the name deserves a straight answer.
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