High-pressure X-ray diffraction studies on - and ?-Mg2SiO4

Abstract Pressure effects on the lattice parameters of β- and γ-Mg 2 SiO 4 have been measured at room temperature and at pressures up to 100 kbar using a multi-anvil high-pressure X-ray diffraction apparatus. The volume changes ( ΔV / V 0 ) at 90 kbar are 5.4 · 10 −2 and 4.2 · 10 −2 for β- and γ-Mg 2 SiO 4 , respectively. Isothermal bulk moduli at zero pressure have been calculated from least-square fits of the data to straight lines. They turn out to be 1.66 ± 0.4 and 2.13 ± 0.1 Mbar for β- and γ-Mg 2 SiO 4 , respectively. The α → γ transition obeys Wang's linear V φ − ρ relation but the α → β transition does not.