Hollandite

Hollandite
General
Category	Oxide minerals
Formula (repeating unit)	Ba(Mn^4+6Mn^3+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]

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.

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

References

1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
2. "Hollandite". Mindat.org. Retrieved 15 February 2022.
3. Mindat.org
4. Mindat.org
5. Mindat.org
6. "Archived copy". Archived from the original on 2017-04-02. Retrieved 2017-04-01.
7. "Hollandite" (PDF). Rruff.info. p. 252. Retrieved 15 February 2022.
8. Post JE, Von Dreele RB, Buseck P (1982) Acta Crystallographica B38: 1056-1065