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 7, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: brownish black.
- 3Read the lusterHold the specimen under a strong light. Luster: dull.
- 4Match the color rangeCompare against the expected color range: brownish gray, gray brown, dark brown gray.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: massive.
Often confused with
Manjiroite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Manjiroite is noticeably harder (Mohs 7 vs. 6); streak differs, so Manjiroite leaves brownish black, Hollandite leaves black; luster reads dull on Manjiroite and metallic, splendent on Hollandite.
How to tell apart: Luster reads dull on Manjiroite and metallic to dull on Cryptomelane.
How to tell apart: Manjiroite is noticeably harder (Mohs 7 vs. 5-6); luster reads dull on Manjiroite and submetallic on Psilomelane.
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(Mn₇Mn)O₁₆
- Mohs hardness
- 7
- Density
- 4.29 g/cm³
- Colors
- Streak
- Brownish black
- Luster
- Dull
- Transparency
- Opaque
- Crystal system
- Tetragonal
- Crystal habit
- Massive
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In the oxidation zone of metamorphosed bedded manganese deposits
Where rockhounds find manjiroite
Classic worldwide localities
- Prompter mine, Tombstone, Cochise Co., Arizona, USA
- Kohare, Tachikawa, Kotamagawa, Kawai, and Takinosawa mines, Iwate Prefecture, Japan
- Bollier, Mary Valley, Queensland, and the Pilbara manganese belt, Western Australia
- Found in the Capillitas mine, Veta Balaza, Catamarca, Argentina
- Adams mine, near Kuruman, Cape Province, South Africa
Field-hunting tip
Where it forms: In the oxidation zone of metamorphosed bedded manganese deposits. If you start seeing pyrolusite, nsutite, birnessite in float, you are in the right ground. Typical habit: massive. 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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