The crystal structures of Mg2 Fe2 C4 O13 , with tetrahedrally coordinated carbon, and Fe13 O19 , synthesized at deep mantle conditions
Articolo
Data di Pubblicazione:
2015
Citazione:
The crystal structures of Mg2 Fe2 C4 O13 , with tetrahedrally coordinated carbon, and Fe13 O19 , synthesized at deep mantle conditions / M. Merlini, M. Hanfland, A. Salamat, S. Petitgirard, H. Müller. - In: AMERICAN MINERALOGIST. - ISSN 0003-004X. - 100:8/9(2015), pp. 2001-2004. [10.2138/am-2015-5369]
Abstract:
We simulated the redox decomposition of magnesium-siderite at pressures and temperatures corresponding to the top of the Earth's D″ layer (135 GPa and 2650 K). It transforms into new phases, with unexpected stoichiometry. We report their crystal structure, based on single-crystal synchrotron radiation diffraction on a multi-grain sample, using a charge-flipping algorithm. Mg2 Fe2 (C4 O13 ) is monoclinic, a = 9.822(3), b = 3.9023(13), c = 13.154(5) Å, β = 108.02(3)°, V = 479.4(3) Å3 (at 135 GPa). It contains tetrahedrally coordinated carbon units, corner-shared in truncated C4 O13 chains. Half of the cations are divalent, and half trivalent. The carbonate coexists with a new iron oxide, Fe13 O19 , monoclinic, a = 19.233(2), b = 2.5820(13), c = 9.550(11) Å, β = 118.39(3)°, V = 417.2(5) Å3 (at 135 GPa). It has a stoichiometry between hematite, Fe2O3, and magnetite, Fe3 O4 . The formation of these unquenchable phases indicates, indirectly, the formation of reduced-carbon species, possibly diamond. These structures suggest the ideas that the mineralogy of the lower mantle and D″ region may be more complex than previously estimated. This is especially significant concerning accessory phases of fundamental geochemical significance and their role in ultra-deep iron-carbon redox coupling processes, as well as the iron-oxygen system, which certainly play an important role in the lower mantle mineral phase equilibria.
Tipologia IRIS:
01 - Articolo su periodico
Keywords:
carbonate; high pressure; iron oxide; single-crystal; tetrahedrally coordinated carbon; geochemistry and petrology; geophysics
Elenco autori:
M. Merlini, M. Hanfland, A. Salamat, S. Petitgirard, H. Müller
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