ABSTRACT

Phase behaviours of kalsilite and its related potassium bearing aluminosilicates (orthoclase and leucite) have been investigated in the pressure region between 120 and 300kbar and at about 1, 000°C in a diamond-anvil press coupled with laser heating. Kalsilite, similar to leucite, has been found to decompose into a mixture of the hollandite-type KAlSi₃O₈ plus a proposed high-pressure form of KAlO₂. The transition was observed at loading pressures greater than 170kbar, and it may be accompanied by a 46% increase in the zero-pressure density. Results of this study show that the hollandite-type KAlSi₃O₈ is the only so-far-known potassium bearing silicate which is stable under the lower mantle conditions.