Ottrelite is a manganese-rich member of the chloritoid group typically occurring as small, dark, tabular crystals or micaceous flakes in metamorphic schists. It is most easily identified by its distinctive manganese content, which often imparts a slightly darker, more greenish-black hue compared to standard iron-rich chloritoid.
Is this ottrelite?
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 ottrelite with a known reference. Ottrelite sits at Mohs 6.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Ottrelite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Ottrelite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: dark green, black, gray-green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals, micaceous aggregates, foliated masses.
Often confused with
Ottrelite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside ottrelite
Minerals reported to co-occur with ottrelite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Mn,Fe²⁺,Mg)₂Al₄Si₂O₁₀(OH)₄
- Mohs hardness
- 6.5
- Density
- 3.5 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular Crystals, Micaceous Aggregates, Foliated Masses
- Cleavage
- Perfect On {001}
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- Low to Medium Grade Metamorphosed Pelitic Rocks
- Typical price
- $10-50 per specimen
Where rockhounds find ottrelite
Classic worldwide localities
- Ottrez, Belgium
- Vermont, USA
- New Hampshire, USA
- Norway
- France
Field-hunting tip
Look in low to medium grade metamorphosed pelitic rocks country — that is the host setting where ottrelite typically forms. If you start seeing quartz, muscovite, garnet in float, you are in the right ground. Field specimens usually show a tabular crystals, micaceous aggregates, foliated masses habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ottrelite?+
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How much is ottrelite worth?+
What rocks look like ottrelite?+
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Find ottrelite on the map
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