Mahnertite is a rare sodium calcium potassium arsenate, typically bright blue to emerald-green. It occurs in the oxidized zone of an arsenic-rich copper deposit (Cap Garonne mine, France). Associated minerals include tennantite, covellite and geminite. It was first described from the Cap Garonne mine, near le Pradet, Var, France.

Hardness

2-3

Mohs

Luster

Vitreous

Streak

Pale Blue

Transparency

Translucent

mineralrareGismondine Group family

Mahnertite

Hardness: 2-3
Luster: Vitreous
Streak: Pale Blue
Transparency: Translucent

Is this mahnertite?

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 mahnertite with a known reference. Mahnertite sits at Mohs 2-3, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Mahnertite leaves a pale blue streak.
3
Read the luster
Hold the specimen under a strong light. Mahnertite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: bright blue, emerald-green.
5
Look at form & habit
Crystal system: tetragonal. Typical habit: tabular crystals.

Often found alongside mahnertite

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

All properties

Chemical formula: (Na,Ca,K)Cu₃(AsO₄)₂Cl(H₂O)₃·2H₂O
Mohs hardness: 2-3
Density: 3.33 g/cm³
Colors: Bright Blue Emerald-green
Streak: Pale Blue
Luster: Vitreous
Transparency: Translucent
Crystal system: Tetragonal
Crystal habit: Tabular Crystals
Cleavage: Perfect On {001}
Rarity: Rare
Uses: Collector
Host rock: Alkaline Igneous Rocks

Where rockhounds find mahnertite

Classic worldwide localities

Cap Garonne mine, Var, France

Field-hunting tip

Look in alkaline igneous rocks country, the host setting where mahnertite typically forms. If you start seeing aegirine, analcime, serandite in float, you are in the right ground. Field specimens usually show a tabular crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify mahnertite?+

Mohs hardness is 2-3. It typically shows a vitreous luster. The streak is pale blue. Common colors include bright blue, emerald-green.

Where is mahnertite found?+

Notable localities include Cap Garonne mine, Var, France.

Is mahnertite safe to handle?+

It contains toxic constituents. Contains arsenic, which is toxic if ingested or inhaled as dust. Wash hands thoroughly after handling and avoid creating dust. Handle with care, avoid grinding or breathing dust, and store separately.

What minerals are found with mahnertite?+

Mahnertite commonly co-occurs with Aegirine, Analcime, Serandite, Microcline. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does mahnertite form in?+

Mahnertite typically forms in alkaline igneous rocks. Working float back to the host body is the standard way to chase a fresh occurrence.

What is mahnertite used for?+

Mahnertite is used in collector.

Find mahnertite on the map

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