Chemistry:Hollandite

Short description: Barium manganese oxide mineral

Hollandite
General
Category	Oxide minerals
Formula (repeating unit)	Ba(Mn4+6Mn3+2)O16
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

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.

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.

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  Hollandite star in rare quartz inclusion

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  Polyhedral representation of the 2 x 2 tunnel structure of hollandite. The black atoms represent Ba.

See also

• Manganese dioxide