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 6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: black.
- 3Read the lusterHold the specimen under a strong light. Luster: earthy.
- 4Match the color rangeCompare against the expected color range: black, brownish black.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: botryoidal, massive.
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, Psilomelane leaves brownish black; luster reads earthy on Asbolane and submetallic on Psilomelane.
How to tell apart: Luster reads earthy on Asbolane and metallic on Pyrolusite.
How to tell apart: Asbolane is noticeably harder (Mohs 6 vs. 4); streak differs, so Asbolane leaves black, Manganite leaves reddish brown to nearly black; luster reads earthy 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
- Mn(O,OH)₂·(Co,Ni,Mg,Ca)x(OH)₂x·nH₂O
- Mohs hardness
- 6
- Density
- 2.8-3.0 g/cm³
- Colors
- Streak
- Black
- Luster
- Earthy
- Transparency
- Opaque
- Crystal system
- Hexagonal
- Crystal habit
- Botryoidal, massive
- Cleavage
- Perfect
- Rarity
- Uncommon
- Uses
- Collector, Ore mineral
- Host rock
- As a weathering product in silicic rocks (Russia); in siliceous schists (Kara-Chagyra, Uzbekistan); widespread in residual soils above ultramafic rocks (New Caledonia)
Where rockhounds find asbolane
Classic worldwide localities
- Kamsdorf, Thuringia, Germany
- Lipov and Tyulenev deposits, Middle Ural Mountains, and the Buranov deposit, Southern Ural Mountains, Russia
- Kara-Chagyra, Uzbekistan
- San Luis mine, Chulchucani, Potosi, Bolivia
Field-hunting tip
Where it forms: As a weathering product in silicic rocks (Russia); in siliceous schists (Kara-Chagyra, Uzbekistan); widespread in residual soils above ultramafic rocks (New Caledonia). If you start seeing goethite in float, you are in the right ground. Typical habit: botryoidal, massive. 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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