Compressibility trends of the clinopyroxenes, and in-situ high-pressure single-crystal X-ray diffraction study of jadeite

Abstract

The crystal structure of a natural jadeite, NaAlSi2O6, was studied at room temperature over the pressure range 0-9.17 GPa using single-crystal X-ray diffraction. Unit-cell data were determined at 16 pressures, and intensity data were collected at nine of these pressures. A third-order Birch-Murnaghan equation of state fit to the P-V data yielded V0 = 402.03(2) Å3, K0 = 136.5(14) GPa, and K0' = 3.4(4). Jadeite exhibits strongly anisotropic compression with unit strain axial ratios of 1.00:1.63:2.10. Silicate chains become more O-rotated with pressure, reducing ∠O3-O3-O3 from 174.7(1)° at ambient pressure to 169.2(6)° at 9.17 GPa and bringing the anions of jadeite closer to a cubic closest-packed arrangement. No evidence of a phase transition was observed over the studied pressure range.