Todorokite is a hydrated manganese oxide mineral typically found in sedimentary marine deposits and oxidized hydrothermal zones. It usually occurs as earthy or fibrous masses and crusts, often appearing as a dark, nondescript coating on other rocks. It is highly significant in geology as a major constituent of deep-sea polymetallic nodules.
Is this todorokite?
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 todorokite with a known reference. Todorokite sits at Mohs 1.5-2.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Todorokite leaves a black streak.
- 3Read the lusterHold the specimen under a strong light. Todorokite typically shows a submetallic luster.
- 4Match the color rangeCompare against the expected color range: black, brownish-black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: fibrous, massive, botryoidal, crusts.
Often confused with
Todorokite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Romanèchite is the harder of the two (Mohs 5-6 vs. 1.5-2.5); streak differs, so Todorokite leaves black, Romanèchite leaves shiny brownish black; luster reads submetallic on Todorokite and submetallic to dull on Romanèchite.
How to tell apart: Pyrolusite is the harder of the two (Mohs 6-6.5 vs. 1.5-2.5); luster reads submetallic on Todorokite and metallic on Pyrolusite.
How to tell apart: Manganite is the harder of the two (Mohs 4 vs. 1.5-2.5); streak differs, so Todorokite leaves black, Manganite leaves dark reddish-brown.
Often found alongside todorokite
Minerals reported to co-occur with todorokite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Na,Ca,K,Ba,Sr)Mn₆O₁₂·3H₂O
- Mohs hardness
- 1.5-2.5
- Density
- 3.3-3.6 g/cm³
- Colors
- Streak
- Black
- Luster
- Submetallic
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Fibrous, Massive, Botryoidal, Crusts
- Cleavage
- None
- Rarity
- Common
- Uses
- Collector, Scientific Research
- Host rock
- Sedimentary Manganese Deposits, Marine Manganese Nodules, Hydrothermal Vents
- Typical price
- $10-50 per specimen
Where rockhounds find todorokite
Classic worldwide localities
- Todoroki Mine, Hokkaido, Japan
- Cuba
- Mexico
- Deep sea nodules, Pacific Ocean
Field-hunting tip
Look in sedimentary manganese deposits, marine manganese nodules, hydrothermal vents country, the host setting where todorokite typically forms. If you start seeing birnessite, pyrolusite, goethite in float, you are in the right ground. Field specimens usually show a fibrous, massive, botryoidal, crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
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