Chloritoid is a diagnostic metamorphic mineral often occurring as distinct tabular crystals or rosettes within foliated rocks like schist. Collectors should look for its characteristic dark green to gray color and prominent cleavage planes that distinguish it from the softer, more flexible chlorite group.
Is this chloritoid?
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 chloritoid with a known reference. Chloritoid 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. Streak: white, grayish, or very slightly greenish.
- 3Read the lusterHold the specimen under a strong light. Luster: somewhat pearly on cleavage surfaces.
- 4Match the color rangeCompare against the expected color range: dark green, green gray, green black, grayish black, dark gray.
- 5Look at form & habitCrystal system: triclinic. Typical habit: foliated, massive.
Often confused with
Chloritoid vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Chloritoid is noticeably harder (Mohs 6.5 vs. 2-2.5); luster reads somewhat pearly on cleavage surfaces on Chloritoid and pearly on Chlorite.
How to tell apart: Streak differs, so Chloritoid leaves white, grayish, or very slightly greenish, Ottrélite leaves greenish, grayish; luster reads somewhat pearly on cleavage surfaces on Chloritoid and vitreous to nearly adamantine on cleavages on Ottrélite.
Often found alongside chloritoid
Minerals reported to co-occur with chloritoid. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- FeAl₂OSiO₄(OH)₂
- Mohs hardness
- 6.5
- Density
- 3.46-3.80 g/cm³
- Colors
- Streak
- White, grayish, or very slightly greenish
- Luster
- Somewhat pearly on cleavage surfaces
- Transparency
- Translucent
- Crystal system
- Triclinic
- Crystal habit
- Foliated, massive
- Cleavage
- Perfect on {001}, distinct on {110}; parting on {010}
- Rarity
- Common
- Uses
- Collector
- Host rock
- In regionally metamorphosed pelitic sediments and schists in the biotite, garnet, and lower grade staurolite zones; in quartz-carbonate veins and other hydrothermal environments
Where rockhounds find chloritoid
1 mapped spotsClassic worldwide localities
- Natick, Kent Co., Rhode Island, USA
- Chester, Hampden Co., Massachusetts, USA
- Clove Valley, Duchess Co., New York, USA
- Bull Mountain, Patrick Co., Virginia, USA
- Kosoi Brod, Mramorskii Zavod, south of Yekaterinburg (Sverdlovsk), Ural Mountains, Russia
- Salmchâteau, near Ottré, Ardennes Mountains, Belgium
Field-hunting tip
Where it forms: In regionally metamorphosed pelitic sediments and schists in the biotite, garnet, and lower grade staurolite zones; in quartz-carbonate veins and other hydrothermal environments. If you start seeing muscovite, chlorite, staurolite in float, you are in the right ground. Typical habit: foliated, massive. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in North Carolina. Start trip planning there.
Common questions
How do you identify chloritoid?+
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Can I find chloritoid in the United States?+
What rocks look like chloritoid?+
What minerals are found with chloritoid?+
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Find chloritoid on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
