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 — Manjiroite leaves black, Cryptomelane leaves brownish black.
How to tell apart: Streak differs — 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 — that is 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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