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, so 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, 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.