Hollandite Locality: Sauberg Mine, Ehrenfriedersdorf , Erzgebirge , Saxony , Germany ( Locality at mindat.org ) Field of view 5 mm. Specimen and photo Leon Hupperichs. — Photo: Leon Hupperichs · CC BY-SA 3.0
Hollandite
A barium-bearing manganese oxide whose structure has 2×2 tunnels — namesake of the tunnel-structured hollandite group.
Intro adapted from Wikipedia (CC BY-SA).
Hollandite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula Ba(Mn⁴⁺₆Mn³⁺₂)O₁₆.
It crystallizes in the monoclinic crystal system (space group I2/m). It is a member of the Coronadite structural group.
Key properties: Mohs hardness 6; specific gravity 4.95; Black streak; Metallic, splendent luster; optically biaxial.
IMA symbol Hol, IMA status: approved, named in 1906.
Found as a primary mineral in contact metamorphic manganese ores, and a secondary weathering product of earlier manganese-bearing minerals.
It is found associated with Bixbyite, braunite, piemontite, other manganese oxides.
The name refers to Dr. Thomas Henry Holland (1868-1947), Director of the Indian Geological Survey. Type Material: n.d.