Manjiroite is a rare manganese oxide mineral belonging to the hollandite group. It typically occurs as dense, fibrous black aggregates in manganese-rich environments and is most commonly identified through X-ray diffraction due to its strong similarity to other manganese oxides.
Is this manjiroite?
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 manjiroite with a known reference. Manjiroite sits at Mohs 6-6.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Manjiroite leaves a black streak.
- 3Read the lusterHold the specimen under a strong light. Manjiroite typically shows a submetallic luster.
- 4Match the color rangeCompare against the expected color range: black, brownish black.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: fibrous aggregates, massive, fine-grained masses.
Often confused with
Manjiroite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads submetallic on Manjiroite and metallic on Hollandite.
How to tell apart: Streak differs, so Manjiroite leaves black, Cryptomelane leaves brownish black.
How to tell apart: Streak differs, so Manjiroite leaves black, Romanèchite leaves shiny brownish black; luster reads submetallic on Manjiroite and submetallic to dull on Romanèchite.
Often found alongside manjiroite
Minerals reported to co-occur with manjiroite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Na,K)(Mn⁴⁺,Mn²⁺)₈O₁₆·nH₂O
- Mohs hardness
- 6-6.5
- Density
- 4.56 g/cm³
- Colors
- Streak
- Black
- Luster
- Submetallic
- Transparency
- Opaque
- Crystal system
- Tetragonal
- Crystal habit
- Fibrous Aggregates, Massive, Fine-grained Masses
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Manganese Ore Deposits
- Typical price
- $20-150 thumbnail to miniature specimens
Where rockhounds find manjiroite
Classic worldwide localities
- Tanohata mine, Iwate Prefecture, Japan
- Postmasburg, South Africa
- Kuruman, South Africa
Field-hunting tip
Look in manganese ore deposits country, the host setting where manjiroite typically forms. If you start seeing rhodochrosite, hausmannite, bementite in float, you are in the right ground. Field specimens usually show a fibrous aggregates, massive, fine-grained masses habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find manjiroite on the map
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