What is Hollandite?
Hollandite is a tunnel-structured manganese oxide group mineral, generally black and found in manganese-rich ores and weathering assemblages.
Mineralogy and structure
Reference formula: Ba(Mn4+,Mn3+)8O16. Hollandite-group structures contain large tunnels that host barium, potassium or lead. Natural compositions vary, so the structure shown is a representative hollandite-type oxide rather than a claim about every specimen. Hollandite belongs to the oxides and has a tetragonal crystal system. Typical hardness is 4–6 on the Mohs scale and specific gravity is approximately 4.5–5.0.
Colour and appearance
Typical colours include black, dark grey, brown-black. The usual fibrous, columnar, massive habit and sub-metallic, metallic lustre are useful descriptive features, but colour alone is not diagnostic.
Formation and localities
Hollandite forms in or is associated with manganese ore deposits, hydrothermal veins and supergene weathering zones. Important documented localities include India, Brazil, Australia, South Africa, Japan and the United States.
Collecting and care
Handle as a labelled manganese-bearing ore and avoid cutting, grinding or creating dust.
