Asbolane is a complex manganese oxide mineral often found as an earthy, cobalt-rich variety of psilomelane. It typically occurs as botryoidal or massive coatings on weathered rocks and is a significant indicator of cobalt enrichment in soil profiles.
Is this asbolane?
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 asbolane with a known reference. Asbolane sits at Mohs 5-6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Asbolane leaves a black streak.
- 3Read the lusterHold the specimen under a strong light. Asbolane typically shows a dull luster.
- 4Match the color rangeCompare against the expected color range: black, bluish black, dark gray.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: botryoidal, massive, or earthy.
Often confused with
Asbolane vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Asbolane leaves black, Romanèchite leaves shiny brownish black; luster reads dull on Asbolane and submetallic to dull on Romanèchite.
How to tell apart: Luster reads dull on Asbolane and metallic on Pyrolusite.
How to tell apart: Asbolane is noticeably harder (Mohs 5-6 vs. 4); streak differs, so Asbolane leaves black, Manganite leaves dark reddish-brown; luster reads dull on Asbolane and submetallic on Manganite.
Often found alongside asbolane
Minerals reported to co-occur with asbolane. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Ni,Co)₁₋ᵧ(Mn⁴⁺,Mn³⁺)O₂(OH)₂₋₂ₓ·nH₂O
- Mohs hardness
- 5-6
- Density
- 2.8-3.0 g/cm³
- Streak
- Black
- Luster
- Dull
- Transparency
- Opaque
- Crystal system
- Hexagonal
- Crystal habit
- Botryoidal, Massive, Or Earthy
- Cleavage
- Perfect
- Rarity
- Uncommon
- Uses
- Collector, Ore Mineral
- Host rock
- Weathered Manganese Deposits and Residual Lateritic Soils
- Typical price
- $10-60 for small mineral specimens
Where rockhounds find asbolane
Classic worldwide localities
- New Caledonia
- Democratic Republic of the Congo
- Germany
- Australia
- United States
Field-hunting tip
Look in weathered manganese deposits and residual lateritic soils country, the host setting where asbolane typically forms. If you start seeing limonite, pyrolusite, goethite in float, you are in the right ground. Field specimens usually show a botryoidal, massive, or earthy habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find asbolane on the map
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