Original paper
X-ray single-crystal structural characterization of Na2MgSiO4 with cristobalite-type structure synthesised at 22 GPa and 1800 °C
Sirotkina, Ekaterina A.; Bindi, Luca; Bobrov, Andrey V.; Tamarova, Anastasia; Pushcharovsky, Dmitry Yu.; Irifune, Tetsuo
European Journal of Mineralogy Volume 30 Number 3 (2018), p. 485 - 489
published: Sep 1, 2018
manuscript accepted: Aug 8, 2017
manuscript revision received: Jul 29, 2017
manuscript received: Jul 11, 2017
Abstract
Na2MgSiO4 is a mineralogical phase known in the literature as N2MS and reported in several high-pressure experiments (13.6 < P < 22 GPa) to coexist with wadsleyite, garnet and pyroxene. Although the crystal structure of room-PT Na2MgSiO4 is known, a structural study of the phase recovered in high-pressure experiments has not been done yet. Here we present a chemical and structural study of a crystal of Na2MgSiO4 synthesised in the model system Na2MgSiO4–Mg2SiO4 at 22 GPa and 1800 °C. The compound was found to crystallize with the orthorhombic cristobalite-type structure previously described at room conditions, space group Pna21, with lattice parameters a = 10.8193(8), b = 5.2702(3), c = 7.0598(4) Å, V = 402.55(4) Å3, and Z = 4. The structure was refined to R1 = 0.0184 using 644 observed reflections [Fo > 4σ(Fo)] and 73 parameters. The unit-cell of the phase studied here is nearly identical to that of Na2MgSiO4 synthesised at room conditions, thus indicating that it likely relaxed during the pressure release occurring during quenching.
Keywords
cristobalite-type structure • synthesis • high-pressure experiments • single-crystal X-ray diffraction • sodium-rich phase • Earth’s mantle