Feitknechtite is a rare manganese hydroxide mineral that most commonly occurs as a pseudomorph after pyrochroite. Collectors often find it as earthy or massive coatings in manganese-rich ore deposits, where it is frequently associated with hausmannite.
Is this feitknechtite?
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 feitknechtite with a known reference. Feitknechtite 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: brown.
- 3Read the lusterHold the specimen under a strong light. Luster: dull.
- 4Match the color rangeCompare against the expected color range: brownish black, black.
- 5Look at form & habitCrystal system: trigonal. Typical habit: hexagonal, platy, thin.
Often confused with
Feitknechtite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Manganite is the harder of the two (Mohs 4 vs. 2.5); streak differs, so Feitknechtite leaves brown, Manganite leaves reddish brown to nearly black; luster reads dull on Feitknechtite and submetallic on Manganite.
How to tell apart: Hausmannite is the harder of the two (Mohs 5.5 vs. 2.5); streak differs, so Feitknechtite leaves brown, Hausmannite leaves dark reddish brown; luster reads dull on Feitknechtite and submetallic on Hausmannite.
How to tell apart: Streak differs, so Feitknechtite leaves brown, Pyrochroite leaves white; luster reads dull on Feitknechtite and pearly on cleavages on Pyrochroite.
Often found alongside feitknechtite
Minerals reported to co-occur with feitknechtite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- β-MnO(OH)
- Mohs hardness
- 2.5
- Density
- 3.8 g/cm³
- Colors
- Streak
- Brown
- Luster
- Dull
- Transparency
- Opaque
- Crystal system
- Trigonal
- Crystal habit
- Hexagonal, platy, thin
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In a mixture with hausmannite, formed by supergene oxidation of and replacing earlier pyrochroite
Where rockhounds find feitknechtite
Classic worldwide localities
- Franklin, Sussex Co., New Jersey, USA
- Noda-Tamagawa and Tanohata mines, Iwate Prefecture, Japan
- Hamayokokawa mine, Nagano Prefecture, Japan
- Taguchi mine, Aichi Prefecture, Japan
- Ioi mine, Shiga Prefecture, Japan
- Långban and Pajsberg, Värmland, Sweden
Field-hunting tip
Where it forms: In a mixture with hausmannite, formed by supergene oxidation of and replacing earlier pyrochroite. If you start seeing pyrochroite, hausmannite in float, you are in the right ground. Typical habit: hexagonal, platy, thin. Train your eye for that shape before scanning the outcrop.
Common questions
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Find feitknechtite on the map
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