Hollandite
Hollandite (chemical formula: Ba(Mn4+6Mn3+2)O16) is a manganese oxide mineral. Its structure consists of double chains of MnO6 octahedra delimiting 2 × 2 tunnels. The electrostatic charge created by the Mn3+ for Mn4+ substitution is balanced by cations in the tunnels. Their nature determines the mineral species: Ba for hollandite, K for cryptomelane, Pb for coronadite, Sr for strontiomelane, Tl for thalliomelane, and Na for manjiroite. Pure species are rare and most 2 × 2 tectomanganates contain mixtures of several types of tunnel cations.
| Hollandite | |
|---|---|
| General | |
| Category | Oxide minerals |
| Formula (repeating unit) | Ba(Mn4+6Mn3+2)O16 |
| IMA symbol | Hol |
| Strunz classification | 4.DK.05a |
| Dana classification | 7.9.1.1 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) |
| Space group | Monoclinic H-M symbol: (2/m) Space group: I2/m |
| Identification | |
| Color | Silvery-grey to greyish |
| Cleavage | Distinct / Good, Prismatic |
| Mohs scale hardness | 4 to 6 |
| Density | 4.95 |
A mineral, with the chemical composition BaMn4+6Fe3+2O16, that was first found in the Kajlidongri mine in the Jhabua district of Madhya Pradesh, India, had the name hollandite until it was reclassified as ferrihollandite by the International Mineralogical Association in 2012. Ferrihollandite is the barium-iron (III) endmember of the coronadite group.
- Hollandite star in rare quartz inclusion
- Polyhedral representation of the 2 x 2 tunnel structure of hollandite. The black atoms represent Ba.