ASBOLANE
Asbolane – (Ni,Co)2-xMn4+(O,OH)4·nH2O – is a rarer (or less detected!) hydroxide, forming part of Mn ores and mainly Co (up to 32%) and Ni. It is known as “nickel-bearing wad”.
It is one of the many Mn minerals that, for centuries, have been sheltered under the “umbrella” terms “cryptomelane”, “psilomelane” and “wad”. These terms refer to hard, black, hydrated manganese ores, with varying contents of Co, Ni and Ba, as well as traces of other elements.
Asbolane may contain impurities such as Al, Ca, Fe and Si and shows effervescence with H2O2 (hydrogen peroxide). There is a variety, cuproasbolane, which contains Cu.
Macroscopically, it is very difficult to differentiate the individual minerals that make up these mixtures. They were only recognized with the widespread application of other analytical techniques, especially X-ray Diffraction.
1. Characteristics
Crystal system: Hexagonal.
Color: Blackish-blue to brownish.
Habit: Earthy, massive, botryoidal, microcrystals
Cleavage: No information available.
Tenacity: No information available.
Twinning: No.
Fracture: No information available.
Mohs Hardness: No information available.
Parting: No.
Streak: Black to black-brown.
Lustre: Dull.
Diaphaneity: Opaque.
Density (g/cm³): 3.1 (calculated)
2. Geology and Deposits
It is formed by the weathering of silicic rocks. Occurs in siliceous shale.
It is very common in residual soils developed on ultramafic rocks.
3. Mineral Associations
It is associated with quartz, goethite, allophane, erythrite, crocoite, takovite, birnessite and Cu minerals (malachite, azurite, conicalcite, agardite-(Y)).
4. Transmitted Light Microscopy
This does not apply because asbolan is completely opaque. The literature indicates that it is uniaxial.
5. Reflected Light Microscopy
There is no specific information for asbolane.
Recognition criteria should be associated with observations of reflected light from psilomelane, cryptomelane, hollandite, and coronadite.