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 — 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 — 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 — that is 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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