Montdorite is a rare phyllosilicate mineral belonging to the mica group, primarily found in the volcanic rocks of the Mont-Dore massif in France. It typically occurs as small, delicate, yellow to brown platy crystals that form within vugs or cavities of volcanic host rock.

Hardness

2.5

Mohs

Luster

Pearly

Streak

White

Transparency

Translucent

mineralrareMica Group family

Montdorite

Hardness: 2.5
Luster: Pearly
Streak: White
Transparency: Translucent

No image

Is this montdorite?

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 montdorite with a known reference. Montdorite sits at Mohs 2.5 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Montdorite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Montdorite typically shows a pearly luster.
4
Match the color range
Compare against the expected color range: yellow, brown.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: platy.

Often confused with

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

Often found alongside montdorite

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

All properties

Chemical formula: (K,Na)(Fe²⁺,Mn,Mg)₂(Si,Al)₄O₁₀(OH,F)₂
Mohs hardness: 2.5
Density: 3.02 g/cm³
Colors: Yellow Brown
Streak: White
Luster: Pearly
Transparency: Translucent
Crystal system: Monoclinic
Crystal habit: Platy
Cleavage: Perfect Basal
Rarity: Rare
Uses: Collector
Host rock: Volcanic Rocks
Typical price: $20-100 per specimen

Where rockhounds find montdorite

Classic worldwide localities

Mont-Dore, France

Field-hunting tip

Look in volcanic rocks country — that is the host setting where montdorite typically forms. If you start seeing sanidine, tridymite, magnetite in float, you are in the right ground. Field specimens usually show a platy habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify montdorite?+

Mohs hardness is 2.5. It typically shows a pearly luster. The streak is white. Common colors include yellow, brown.

Where is montdorite found?+

Notable localities include Mont-Dore, France.

How much is montdorite worth?+

Typical asking prices fall in the range of $20-100 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like montdorite?+

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

What minerals are found with montdorite?+

Montdorite commonly co-occurs with Sanidine, Tridymite, Magnetite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does montdorite form in?+

Montdorite typically forms in volcanic rocks. Working float back to the host body is the standard way to chase a fresh occurrence.

What is montdorite used for?+

Montdorite is used in collector.

Find montdorite on the map

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