Berthierine is a clay mineral typically found in marine sedimentary iron deposits, often appearing as massive or earthy, poorly crystalline masses. Because it is chemically and structurally similar to chamosite and other iron-rich chlorites, positive identification usually requires X-ray diffraction analysis. Collectors primarily value it as an accessory mineral associated with oolitic ironstone formations.
Is this berthierine?
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 berthierine with a known reference. Berthierine sits at Mohs 2.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Berthierine leaves a pale green streak.
- 3Read the lusterHold the specimen under a strong light. Berthierine typically shows a dull luster.
- 4Match the color rangeCompare against the expected color range: dark green, brownish green, blackish green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: massive.
Often confused with
Berthierine vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Berthierine leaves pale green, Chlorite leaves white; luster reads dull on Berthierine and pearly on Chlorite.
How to tell apart: Streak differs — Berthierine leaves pale green, Chamosite leaves white to pale green; luster reads dull on Berthierine and pearly on Chamosite.
How to tell apart: Streak differs — Berthierine leaves pale green, Kaolinite leaves white.
Often found alongside berthierine
Minerals reported to co-occur with berthierine. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Fe²⁺,Fe³⁺,Al,Mg)₂(Si,Al)₂O₅(OH)₄
- Mohs hardness
- 2.5
- Density
- 2.6-3.0 g/cm³
- Streak
- Pale Green
- Luster
- Dull
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Massive
- Cleavage
- Perfect Basal
- Rarity
- Common
- Uses
- Collector
- Host rock
- Sedimentary Iron-rich Beds
- Typical price
- $10-50 per specimen
Where rockhounds find berthierine
Classic worldwide localities
- France
- Germany
- USA
- United Kingdom
- Russia
Field-hunting tip
Look in sedimentary iron-rich beds country — that is the host setting where berthierine typically forms. If you start seeing siderite, chamosite, calcite in float, you are in the right ground. Field specimens usually show a massive habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find berthierine on the map
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