Guanacoite is a very rare copper-magnesium arsenate mineral found primarily in the oxidation zones of arsenic-rich ore deposits. It typically forms delicate pale pink tabular crystals or radial clusters and is highly prized by advanced mineral collectors for its scarcity and aesthetic crystal form.
Is this guanacoite?
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 guanacoite with a known reference. Guanacoite 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: white to pale blue.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: blue, pale blue.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic.
Often confused with
Guanacoite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Guanacoite leaves white to pale blue, Clinoclase leaves bluish green.
How to tell apart: Conichalcite is the harder of the two (Mohs 4.5 vs. 3); streak differs, so Guanacoite leaves white to pale blue, Conichalcite leaves green.
Often found alongside guanacoite
Minerals reported to co-occur with guanacoite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- MgCu₂Mg₂(AsO₄)₂(OH)₄(H₂O)₄
- Mohs hardness
- 3
- Density
- 3.29-3.31 g/cm³
- Streak
- White to pale blue
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic
- Cleavage
- Parallel to {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A secondary phase in a high sulfidation-type, Au-rich epithermal deposit hosted by felsic rocks (El Guanaco mine), weathered in an arid and Mg-rich environment
Where rockhounds find guanacoite
Classic worldwide localities
- El Guanaco mine, ~93 km east of Taltal and 230 km southeast of Antofagasta, 2nd Region, northern Chile and at Taghouni (Tarouni), Bou Azzer district, Morocco
Field-hunting tip
Where it forms: A secondary phase in a high sulfidation-type, Au-rich epithermal deposit hosted by felsic rocks (El Guanaco mine), weathered in an arid and Mg-rich environment. If you start seeing arhbarite, conichalcite, olivenite in float, you are in the right ground. Typical habit: prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify guanacoite?+
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Is guanacoite safe to handle?+
What rocks look like guanacoite?+
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Find guanacoite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
