Atacamite is a striking copper chloride mineral known for its vivid, intense green color. It typically forms as a secondary mineral in the oxidized zones of copper deposits, often found as radiating sprays of acicular crystals or crusts within arid, desert environments.
Is this atacamite?
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 atacamite with a known reference. Atacamite sits at Mohs 3-3.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: apple-green.
- 3Read the lusterHold the specimen under a strong light. Luster: adamantine to vitreous.
- 4Match the color rangeCompare against the expected color range: dark green, bright green, emerald green, green, yellow, yellow green, black green.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: euhedral crystals, fibrous, granular.
Often confused with
Atacamite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Atacamite leaves apple-green, Malachite leaves pale green.
How to tell apart: Streak differs, so Atacamite leaves apple-green, Brochantite leaves pale green; luster reads adamantine to vitreous on Atacamite and vitreous, somewhat pearly on cleavages on Brochantite.
How to tell apart: Streak differs, so Atacamite leaves apple-green, Libethenite leaves light green; luster reads adamantine to vitreous on Atacamite and vitreous, greasy on fracture surfaces on Libethenite.
Often found alongside atacamite
Minerals reported to co-occur with atacamite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu₂Cl(OH)₃
- Mohs hardness
- 3-3.5
- Density
- 3.745-3.776 g/cm³
- Streak
- Apple-green
- Luster
- Adamantine to vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Euhedral crystals, fibrous, granular
- Cleavage
- {010}, perfect; {101}, fair
- Rarity
- Uncommon
- Uses
- Collector, Scientific research
- Host rock
- An oxidation product of other copper minerals, especially under arid, saline conditions; in fumarolic deposits; a weathering product of sulfides in subsea black smoker deposits
Where rockhounds find atacamite
1 mapped spotsClassic worldwide localities
- Bisbee, Cochise Co., in Santa Cruz porphyry deposit, in the Mammoth-St. Anthony mine, Tiger, and in the San Manuel mine, Pinal Co., Arizona, USA
- Tintic district, Juab Co., Utah, USA
- Now known from many places, as at Copiapó, Carrizal, Tierra Amarilla, and Remolinos, Atacama, Chile
- Collahurasi, Tarapacá, Chile
- Chuquicamata, Antofagasta, Chile
- Boleo, Baja California, Mexico
Field-hunting tip
Where it forms: An oxidation product of other copper minerals, especially under arid, saline conditions; in fumarolic deposits; a weathering product of sulfides in subsea black smoker deposits. If you start seeing cuprite, brochantite, linarite in float, you are in the right ground. Typical habit: euhedral crystals, fibrous, granular. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in New Mexico. Start trip planning there.
Common questions
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Find atacamite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
