Chamosite is an iron-rich member of the chlorite group that commonly forms as an alteration product in marine sedimentary environments. It is most often found as green, clay-like, earthy masses or fine micaceous coatings, frequently associated with oolitic iron ores.
Is this chamosite?
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 chamosite with a known reference. Chamosite sits at Mohs 3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Chamosite leaves a white to pale green streak.
- 3Read the lusterHold the specimen under a strong light. Chamosite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: green, grayish-green, blackish-green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: micaceous, platy, or massive aggregates.
Often confused with
Chamosite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Chamosite leaves white to pale green, Clinochlore leaves white.
How to tell apart: Chamosite is noticeably harder (Mohs 3 vs. 2); streak differs — Chamosite leaves white to pale green, Pennantite leaves white.
How to tell apart: Streak differs — Chamosite leaves white to pale green, Biotite leaves white.
Often found alongside chamosite
Minerals reported to co-occur with chamosite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Fe²⁺,Mg,Fe³⁺)₅Al(Si₃Al)O₁₀(OH,O)₈
- Mohs hardness
- 3
- Density
- 3.0-3.4 g/cm³
- Streak
- White to Pale Green
- Luster
- Pearly
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Micaceous, Platy, Or Massive Aggregates
- Cleavage
- Perfect Basal
- Rarity
- Common
- Uses
- Collector, Geological Study
- Host rock
- Sedimentary Ironstones and Low-grade Metamorphic Rocks
- Typical price
- $10-50 per specimen
Where rockhounds find chamosite
Classic worldwide localities
- Chamoson, Switzerland
- Lorraine, France
- Cornwall, England
- Appalachian region, USA
Field-hunting tip
Look in sedimentary ironstones and low-grade metamorphic rocks country — that is the host setting where chamosite typically forms. If you start seeing siderite, hematite, quartz in float, you are in the right ground. Field specimens usually show a micaceous, platy, or massive aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find chamosite on the map
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