Thermal equation of state of a natural kyanite up to 8.55Â GPa and 1273Â K

The thermal equation of state of a natural kyanite has been investigated with a DIA-type, cubic-anvil apparatus (SAM85) combined with an energy-dispersive synchrotron X-ray radiation technique up to 8.55 GPa and 1273 K. No phase transition was observed in the studied pressure-temperature (P-T) range. The Le Bail full profile refinement technique was used to derive the unit-cell parameters. By fixing the bulk modulus K0 as 196 GPa and its pressure derivative K0′ as 4, our P-V (volume)-T data were fitted to the high temperature Birch-Murnaghan equation of state. The obtained parameters for the kyanite are: V0 = 294.05(9) Å3, α = 2.53(11) × 10−5 K−1 and (∂K/∂T)P = −0.021(8) GPa∙K−1. These parameters have been combined with other experimentally-measured thermodynamic data for the relevant phases to calculate the P-T locus of the reaction kyanite = stishovite + corundum. With this thermodynamically constrained phase boundary, previous high-pressure phase equilibrium experimental studies with the multi-anvil press have been evaluated.