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 — 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 — 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 — that is 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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Find todorokite on the map
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