HOLLANDITE (miniature)

Hollandite, with the chemical formula Ba(Mn4+6Mn3+2)O16, is a manganese oxide mineral characterized by its unique structure, which features double chains of MnO6 octahedra that create 2 × 2 tunnels. The electrostatic charge resulting from the substitution of Mn3+ for Mn4+ is neutralized by cations located within these tunnels, and the specific type of cation present defines the mineral species: barium for hollandite, potassium for cryptomelane, lead for coronadite, strontium for strontiomelane, thallium for thalliomelane, and sodium for manjiroite. Pure forms of these minerals are uncommon, as most 2 × 2 tectomanganates consist of various tunnel cation mixtures. A mineral initially identified as hollandite, with the composition BaMn4+6Fe3+2O16, was discovered in the Kajlidongri mine in Madhya Pradesh, India. However, in 2012, the International Mineralogical Association reclassified it as ferrihollandite, which represents the barium-iron (III) endmember of the coronadite group.

From the former SUMMIT MINERALS Collection Alburquerque