Abstract
To map the stability field of calcium ferrite-type MgAl2O4-Mg2SiO4 solid solutions, high-pressure phase relations in the system MgAl2O4-Mg2SiO4 were studied in the compositional range of 0 to 50 mol% Mg2SiO4. The calcium ferrite solid solutions are stable above 23 GPa at 1600 °C, and the maximum solubility of Mg2SiO4 component in MgAl2O4 calcium ferrite is 34 mol%. Lattice parameters and unit-cell volume of calcium ferrite-type MgAl2O4 (space group Pbnm) determined by Rietveld analysis are a = 9.9498(6) Å, b = 8.6468(6) Å, c = 2.7901(2) Å, and V = 240.02(2) Å3. Lattice parameters for the MgAl2O4-Mg2SiO4 solid solutions with the compositions of 14, 24, and 34 mol% Mg2SiO4 indicated the following compositional dependency of lattice parameters: a (Å) = 9.9498 + 0.1947·XMg₂SiO₄, b (Å) = 8.6468 . 0.1097·XMg₂SiO₄, and c (Å) = 2.7901 + 0.0086·XMg₂SiO₄, where XMg2SiO4 is the mole fraction of Mg₂SiO₄ component. A linear extrapolation of the composition-molar volume relationship gave an estimated volume of 36.49(2) cm3/mol for the hypothetical calcium ferrite-type Mg2SiO4. This value is larger than that of the isochemical mixture of MgSiO3 perovskite and MgO, 35.72(1) cm3/mol. This implies that the mixture of MgSiO3 perovskite and MgO is more stable than the hypothetical calcium ferrite-type Mg2SiO4 under the lower mantle conditions.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
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- Dehydration of Ca-montmorillonite at the crystal scale. Part I: Structure evolution
- Dehydration of Ca-montmorillonite at the crystal scale. Part 2. Mechanisms and kinetics
- The high-pressure crystal structure of potassium hydrogen carbonate (KHCO3)
- Effect of Al3+ and H+ on the elastic properties of stishovite
- Investigation of synthetic Mg1.3V1.7O4 spinel with MgO inclusions: Case study of a spinel with an apparently occupied interstitial site
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- Compression, thermal expansion, structure, and instability of CaIrO3, the structure model of MgSiO3 post-perovskite
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- The energetics of hematite dissolution in iron-oxide-rich melts: In situ high-temperature calorimetric studies
- A simple model of oscillatory zoning in magmatic plagioclase: Development of an isothermal undercooling model
- TEM investigation of Ca-rich plagioclase: Structural β uctuations related to the I1-P1 phase transition
- Crystal-chemistry of Ni in marine ferromanganese crusts and nodules
- Effect of structural transitions on properties of high-pressure silicate melts: 27Al NMR, glass densities, and melt viscosities
- Material conversion from paper-sludge ash in NaOH, KOH, and LiOH solutions
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- Origin of atoll garnets in eclogites and implications for the redistribution of trace elements during slab exhumation in a continental subduction zone
- Determination of the refractive index of particles in the clay and sub-micrometer size range
- Crystal chemistry of synthetic Ca2Al3Si3O12OH–Sr2Al3Si3O12OH solid-solution series of zoisite and clinozoisite
- Thermal infrared spectroscopy and modeling of experimentally shocked basalts
- P-V and T-V Equations of State of natural biotite: An in-situ high-pressure and high-temperature powder diffraction study, combined with Mössbauer spectroscopy
- Cation ordering in MgTi2O5 (karrooite): Probing temperature dependent effects with neutrons
- An order-disorder model for omphacitic pyroxenes in the system jadeite-diopsidehedenbergite- acmite, with applications to eclogitic rocks
- The high-pressure structural configurations of Ca0.2Sr0.8Al2Si2O8 feldspar: The I1̅-I2/c and I2/c-P21/c phase transitions
- Mechanisms of diamond oxidation and their bearing on the fluid composition in kimberlite magmas
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