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.

Hardness

3.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Guanacoite

Hardness: 3.5
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this guanacoite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch guanacoite with a known reference. Guanacoite sits at Mohs 3.5 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Guanacoite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Guanacoite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: pale pink, pinkish-white, colorless.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: tabular crystals, radial aggregates, crusts.

Often confused with

Guanacoite vs. its common look-alikes — and how to tell them apart in the field.

mineral

Clinoclase

Mohs 2.5-3

How to tell apart: Streak differs — Guanacoite leaves white, Clinoclase leaves bluish-green.

How to tell apart: Conichalcite is the harder of the two (Mohs 4.5 vs. 3.5); streak differs — Guanacoite leaves white, Conichalcite leaves light green.

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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: Mg₂Cu₆(AsO₄)₄(OH)₄·5H₂O
Mohs hardness: 3.5
Density: 3.2 g/cm³
Colors: Pale Pink Pinkish-white Colorless
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Tabular Crystals, Radial Aggregates, Crusts
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Hydrothermal Veins
Typical price: $50-300 per specimen

Where rockhounds find guanacoite

Classic worldwide localities

Guanaco Mine, Antofagasta, Chile

Field-hunting tip

Look in hydrothermal veins country — that is the host setting where guanacoite typically forms. If you start seeing austinite, quartz, arsenates in float, you are in the right ground. Field specimens usually show a tabular crystals, radial aggregates, crusts habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify guanacoite?+

Mohs hardness is 3.5. It typically shows a vitreous luster. The streak is white. Common colors include pale pink, pinkish-white, colorless.

Where is guanacoite found?+

Notable localities include Guanaco Mine, Antofagasta, Chile.

How much is guanacoite worth?+

Typical asking prices fall in the range of $50-300 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

Is guanacoite safe to handle?+

It contains toxic constituents. Contains arsenic, a toxic element. Handle with care, wash hands after touching, and avoid creating dust when breaking specimens. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like guanacoite?+

Guanacoite is most often confused with Clinoclase, Conichalcite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with guanacoite?+

Guanacoite commonly co-occurs with Austinite, Quartz, Arsenates. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does guanacoite form in?+

Guanacoite typically forms in hydrothermal veins. Working float back to the host body is the standard way to chase a fresh occurrence.

What is guanacoite used for?+

Guanacoite is used in collector.

Find guanacoite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.