Hollandite

Hollandite (chemical formula: Ba(Mn⁴⁺₆Mn³⁺₂)O₁₆) is a manganese oxide mineral.^[2] 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,^[3] Tl for thalliomelane,^[4] and Na for manjiroite.^[5] Pure species are rare and most 2 × 2 tectomanganates contain mixtures of several types of tunnel cations.

Hollandite
General
Category	Oxide minerals
Formula	Ba(Mn4+6Mn3+2)O16
IMA symbol	Hol[1]
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[2]

A mineral, with the chemical composition BaMn⁴⁺₆Fe³⁺₂O₁₆,^[6] that was first found in the Kajlidongri mine in the Jhabua district of Madhya Pradesh, India,^[7] 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.^[2]

• 
  Hollandite star in rare quartz inclusion

• 
  Polyhedral representation of the 2 x 2 tunnel structure of hollandite. The black atoms represent Ba.^[8]

See also

• Manganese dioxide