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.
Is this sudoite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch sudoite with a known reference. Sudoite sits at Mohs 2.5-3.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: pearly.
- 4Match the color rangeCompare against the expected color range: white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: granular.
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, Clinochlore leaves greenish white to white.
How to tell apart: Streak differs, so Sudoite leaves white, Chamosite leaves green to gray.
How to tell apart: Luster reads pearly on Sudoite and vitreous to pearly or silky on Muscovite.
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
- Mg₂Al₃(Si₃Al)O₁₀(OH)₈
- Mohs hardness
- 2.5-3.5
- Density
- 2.63-2.68 g/cm³
- Colors
- Streak
- White
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Granular
- Cleavage
- Perfect on {001}
- Rarity
- Uncommon
- Uses
- Collector, Scientific research
- Host rock
- Disseminated in hematite ore, probably of hydrothermal origin (Negaunee, Michigan, USA); an authigenic mineral in aeolian sandstones (Kesselberg, Germany); in low-grade metamorphic assemblages (Ottré, Belgium)
Where rockhounds find sudoite
Classic worldwide localities
- Tracy mine, Negaunee, Marquette Co., Michigan, USA
- Lützelbach, near Plochingen, Baden-Württemberg, Germany
- Kesselberg area, Black Forest, Germany
- Biesenrode, Harz Mountains, Germany
- Ottré, near Salmchâteau, Ardennes Mountains, Belgium
- Beresov, Ural Mountains, Russia
Field-hunting tip
Where it forms: Disseminated in hematite ore, probably of hydrothermal origin (Negaunee, Michigan, USA); an authigenic mineral in aeolian sandstones (Kesselberg, Germany); in low-grade metamorphic assemblages (Ottré, Belgium). If you start seeing hematite, quartz, carpholite in float, you are in the right ground. Typical habit: granular. Train your eye for that shape before scanning the outcrop.
Common questions
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Find sudoite on the map
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