Sudoite is a di-trioctahedral chlorite mineral, historically referred to as an Al-rich chlorite or dioctahedral-trioctahedral chlorite. Collectors typically find it as white or gray micaceous scales or platy aggregates often associated with alteration zones in volcanic rocks.

Hardness

2.5-3

Mohs

Luster

Pearly

Streak

White

Transparency

Translucent

mineraluncommonChlorite Group family

Sudoite

Hardness: 2.5-3
Luster: Pearly
Streak: White
Transparency: Translucent

Is this sudoite?

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

Often confused with

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

How to tell apart: Streak differs — Sudoite leaves white, Chamosite leaves white to pale green.

Often found alongside sudoite

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

All properties

Chemical formula: Mg₂(Al,Fe³⁺,Mg)₃(Si₃Al)O₁₀(OH)₈
Mohs hardness: 2.5-3
Density: 2.5-2.7 g/cm³
Colors: White Gray Greenish
Streak: White
Luster: Pearly
Transparency: Translucent
Crystal system: Monoclinic
Crystal habit: Platy Crystals, Micaceous Masses, Scaly Aggregates
Cleavage: Perfect Basal
Rarity: Uncommon
Uses: Collector, Scientific Research
Host rock: Hydrothermal Veins, Metamorphic Rocks, Weathered Volcanic Rocks
Typical price: $10-50 per specimen

Where rockhounds find sudoite

Classic worldwide localities

Sudo, Japan
Belledonne Massif, France
Kola Peninsula, Russia
Hartz Mountains, Germany

Field-hunting tip

Look in hydrothermal veins, metamorphic rocks, weathered volcanic rocks country — that is the host setting where sudoite typically forms. If you start seeing quartz, pyrite, kaolinite in float, you are in the right ground. Field specimens usually show a platy crystals, micaceous masses, scaly aggregates habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify sudoite?+

Mohs hardness is 2.5-3. It typically shows a pearly luster. The streak is white. Common colors include white, gray, greenish.

Where is sudoite found?+

Notable localities include Sudo, Japan; Belledonne Massif, France; Kola Peninsula, Russia; Hartz Mountains, Germany.

How much is sudoite worth?+

Typical asking prices fall in the range of $10-50 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like sudoite?+

Sudoite is most often confused with Clinochlore, Chamosite, Muscovite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with sudoite?+

Sudoite commonly co-occurs with Quartz, Pyrite, Kaolinite, Chlorite group minerals. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does sudoite form in?+

Sudoite typically forms in hydrothermal veins, metamorphic rocks, weathered volcanic rocks. Working float back to the host body is the standard way to chase a fresh occurrence.

What is sudoite used for?+

Sudoite is used in collector, scientific research.

Find sudoite on the map

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