Tondiite is a rare copper magnesium chloride hydroxide mineral found in the oxidation zones of copper-bearing deposits. It typically forms as small, dark green platy crystals or granular masses that can easily be mistaken for other members of the atacamite group.

Hardness

3-3.5

Mohs

Luster

Vitreous

Transparency

Transparent

mineralrareAtacamite Group family

Tondiite

Hardness: 3-3.5
Luster: Vitreous
Transparency: Transparent

Is this tondiite?

4-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 tondiite with a known reference. Tondiite sits at Mohs 3-3.5, softer than the next harder reference, harder than the previous one.
2
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
3
Match the color range
Compare against the expected color range: emerald green, bright green.
4
Look at form & habit
Crystal system: trigonal. Typical habit: platy crystals, granular aggregates.

Often confused with

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

mineral

Atacamite

Mohs 3-3.5

How to tell apart: Luster reads vitreous on Tondiite and adamantine to vitreous on Atacamite.

How to tell apart: Luster reads vitreous on Tondiite and adamantine to vitreous on Clinoatacamite.

Compare →

Often found alongside tondiite

Minerals reported to co-occur with tondiite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: Cu₃Mg(OH)₆Cl₂
Mohs hardness: 3-3.5
Density: 3.503 g/cm³
Colors: Emerald green Bright green
Luster: Vitreous
Transparency: Transparent
Crystal system: Trigonal
Crystal habit: Platy crystals, granular aggregates
Rarity: Rare
Uses: Collector
Host rock: A secondary mineral in vesicles in phonolitic tephrite (Vesuvius); a secondary oxidation product of chalcocite, bornite and chalcopyrite in an environment rich in Cl in andesitic porphyric lavas and lava tuff (Chile)

Where rockhounds find tondiite

Classic worldwide localities

Vesuvius volcano, Italy, and from the Santo Domingo Cu Mine, Caleta Vitor district, Arica Province, Chile

Field-hunting tip

Where it forms: A secondary mineral in vesicles in phonolitic tephrite (Vesuvius); a secondary oxidation product of chalcocite, bornite and chalcopyrite in an environment rich in Cl in andesitic porphyric lavas and lava tuff (Chile). If you start seeing leucite, sodalite, nepheline in float, you are in the right ground. Typical habit: platy crystals, granular aggregates. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify tondiite?+

Mohs hardness is 3-3.5. Luster: vitreous. Common colors include emerald green, bright green.

Where is tondiite found?+

Notable localities include Vesuvius volcano, Italy, and from the Santo Domingo Cu Mine, Caleta Vitor district, Arica Province, Chile.

Is tondiite safe to handle?+

Tondiite contains copper. Contains copper; wash hands thoroughly after handling and avoid ingestion or inhalation of dust. Proper storage is advised due to potential sensitivity to moisture.

What rocks look like tondiite?+

Tondiite is most often confused with Atacamite, Paratacamite, Clinoatacamite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with tondiite?+

Tondiite commonly co-occurs with Leucite, Sodalite, Nepheline, Sanidine, Haydeeite, Anhydrite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does tondiite form in?+

Where it forms: A secondary mineral in vesicles in phonolitic tephrite (Vesuvius); a secondary oxidation product of chalcocite, bornite and chalcopyrite in an environment rich in Cl in andesitic porphyric lavas and lava tuff (Chile). Working float back to the host body is the standard way to chase a fresh occurrence.

What is tondiite used for?+

Tondiite is used in collector.

Find tondiite on the map

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