Bosoite is an amorphous manganese oxide mineral often found as black coatings or botryoidal masses within manganese-rich sedimentary deposits. It is frequently indistinguishable from other 'wad' or psilomelane-group minerals without chemical analysis. Collectors typically find it as an accessory mineral in manganese ore beds.
Is this bosoite?
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 bosoite with a known reference. Bosoite sits at Mohs 3-4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Bosoite leaves a black streak.
- 3Read the lusterHold the specimen under a strong light. Bosoite typically shows a dull luster.
- 4Match the color rangeCompare against the expected color range: black.
- 5Look at form & habitCrystal system: amorphous. Typical habit: massive, crusts, or globular aggregates.
Often confused with
Bosoite 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. 3-4); streak differs, so Bosoite leaves black, Romanèchite leaves shiny brownish black; luster reads dull on Bosoite and submetallic to dull on Romanèchite.
How to tell apart: Pyrolusite is the harder of the two (Mohs 6-6.5 vs. 3-4); luster reads dull on Bosoite and metallic on Pyrolusite.
Often found alongside bosoite
Minerals reported to co-occur with bosoite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- MnO₂·nH₂O
- Mohs hardness
- 3-4
- Density
- 2.2-2.5 g/cm³
- Colors
- Streak
- Black
- Luster
- Dull
- Transparency
- Opaque
- Crystal system
- Amorphous
- Crystal habit
- Massive, Crusts, Or Globular Aggregates
- Cleavage
- None
- Rarity
- Common
- Uses
- Collector
- Host rock
- Sedimentary Manganese Deposits
- Typical price
- $5-30 for cabinet specimens
Where rockhounds find bosoite
Classic worldwide localities
- Boso Peninsula, Japan
- Various sedimentary manganese deposits globally
Field-hunting tip
Look in sedimentary manganese deposits country, the host setting where bosoite typically forms. If you start seeing quartz, calcite, goethite in float, you are in the right ground. Field specimens usually show a massive, crusts, or globular aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find bosoite on the map
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