Hollandite II phase in KAlSi3O8 as a potential host mineral of potassium in the Earth's lower mantle

Naohisa Hirao, Eiji Ohtani, Tadashi Kondo, Takeshi Sakai, Takumi Kikegawa

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22 Citations (Scopus)


High-pressure and high-temperature experiments on the KAlSi3O8 composition were conducted in a laser-heated diamond-anvil cell at pressures up to 128 GPa, which correspond to the lowermost mantle conditions. In situ synchrotron X-ray diffraction measurements revealed that the hollandite II phase in KAlSi3O8 with a monoclinic symmetry of I2/m was stable over the entire range of mantle conditions, and the tunnel structure formed by the double chains of edge-sharing (Si,Al)O6 octahedra, which could accommodate a larger cation such as potassium, was sustained. The (Si,Al)O6 octahedra in the KAlSi3O8 hollandite II phase showed a similar compression behavior to those in high-pressure silicate structures, such as rutile-type and perovskite-type phases, and were found to be less compressible than the KO8 polyhedra. The KAlSi3O8 hollandite II phase is a potential host mineral for potassium under lower mantle conditions and, therefore, may have a significant influence on geochemistry if potassium feldspar KAlSi3O8 in the Earth's crust is transported into the Earth's mantle through subduction.

Original languageEnglish
Pages (from-to)97-104
Number of pages8
JournalPhysics of the Earth and Planetary Interiors
Issue number1-2
Publication statusPublished - 2008 Jan
Externally publishedYes


  • Diamond-anvil cell
  • Earth's lower mantle
  • Hollandite II phase
  • KAlSiO

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Geophysics
  • Physics and Astronomy (miscellaneous)
  • Space and Planetary Science


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