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. Streak: greenish white.
- 3Read the lusterHold the specimen under a strong light. Luster: pearly.
- 4Match the color rangeCompare against the expected color range: dark green, brown green, green yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: microscopic crystals, oolitic.
Often confused with
Berthierine vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Berthierine leaves greenish white, Chlorite leaves white.
How to tell apart: Streak differs, so Berthierine leaves greenish white, Chamosite leaves green to gray.
How to tell apart: Streak differs, so Berthierine leaves greenish white, 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
- (Fe,Fe,Al)₃(Si,Al)₂O₅(OH)₄
- Mohs hardness
- 2.5
- Density
- 3.03 g/cm³
- Streak
- Greenish white
- Luster
- Pearly
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Microscopic crystals, oolitic
- Cleavage
- Perfect basal
- Rarity
- Common
- Uses
- Collector
- Host rock
- Common in unmetamorphosed marine sediments; in lateritic and polar soils
Where rockhounds find berthierine
Classic worldwide localities
- Hayange, Meurthe-et-Moselle, France
- Stanion Lane pit, Corby, Northamptonshire, England
- Worth Farm and in the Philpots quarry, West Sussex, England
- Belgorod district and the Voronezh anticline, Kursk, Russia
- Chichibu mine, Saitama Prefecture, Japan
- Ellef Ringnes Island, Northwest Territories, Canada
Field-hunting tip
Where it forms: Common in unmetamorphosed marine sediments; in lateritic and polar soils. If you start seeing glauconite, siderite, calcite in float, you are in the right ground. Typical habit: microscopic crystals, oolitic. 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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