Stability of KAlSi3O8 Hollandite‐type structure in the Earth's lower mantle conditions

The stability of KAISi3O8 hollandite-type structure is investigated in a series of synthesis experiments between 20 and 95 GPa at 650(±50) °C and between 1200 to 2300 °C, using electrically- and laser-heated diamond anvil cells, respectively. Potassium feldspar transformed to a hollandite-type structure in the experimental pressure range from 20 to 95 GPa at temperatures between 1200 to 2300 °C, whereas it remained amorphous at 65(±5) GPa and 650(±50) °C. KAISi3O8 hollandite is, therefore, a stable phase under the pressure and temperature conditions of at least 2200 km deep in the lower mantle and could be an important host for potassium in that region.