Skip to content
Licensed Unlicensed Requires Authentication Published by De Gruyter September 20, 2020

Si-rich Mg-sursassite Mg4Al5Si7O23(OH)5 with octahedrally coordinated Si: A new ultrahigh-pressure hydrous phase

  • Luca Bindi ORCID logo , Mark D. Welch , Aleksandra A. Bendeliani and Andrey V. Bobrov
From the journal American Mineralogist


The crystal structure of a new high-pressure hydrous phase, Si-rich Mg-sursassite, of ideal composition Mg4Al5Si7O23(OH)5, that was produced by sub-solidus reaction at 24 GPa and 1400 °C in an experiment using a model sedimentary bulk composition, has been determined by single-crystal X‑ray diffraction. The phase was found to be topologically identical to Mg-sursassite, Mg5Al5Si6O21(OH)7, and has space group P21/m and lattice parameters a = 8.4222(7), b = 5.5812(3), c = 9.4055(9) Å, β = 106.793(8)°, V = 423.26(6) Å3, and Z = 1. The empirical formula determined by electron microprobe analysis of the same crystal as was used in the X‑ray experiment is [Mg3.93(3)Fe0.03(1)]S3.96[Al4.98(3)Cr0.04(1)]S5.02 Si7.02(4)O23(OH)5, with hydroxyl content implied by the crystal-structure analysis. The most significant aspect of the structure of Si-rich Mg-sursassite is the presence of octahedrally coordinated Si. Its structural formula is M1,VIIMg2M2VIMg22+M3,VI(Al0.5Si0.5)2M4,VIAl2M5,VIAl2T1,IVSi2T2,IVSi2T3,IVSi2O23(OH)5.Si-rich Mg-sursassite joins the group of hydrous ultrahigh-pressure phases with octahedrally coordinated Si that have been discovered by experiment, and that may play a significant role in the distribution and hosting of water in the deep mantle at subduction zones. The reactions defining the stability of Si-rich Mg-sursassite are unknown, but are likely to be fundamentally diferent from those of Mg-sursassite, and involve other ultrahigh-pressure dense structures such as phase D, rather than phase A.

Acknowledgments and Funding

The paper benefited by the official reviews from Wilson Crichton and an anonymous reviewer. These experiments were a part of the scientific program of the Laboratory of Deep Geospheres, Geological Faculty, Moscow State University and were supported by the Russian Science Foundation, project no. 17-17-01169. A.A.B. thanks the Geodynamics Research Center, Ehime University, Matsuyama, Japan, for support of her visit in 2019.

References cited

Brese, N.E., and O’Keeffe, M. (1991) Bond-valence parameters for solids. Acta Crystallographica, B47, 192–197.10.1107/S0108768190011041Search in Google Scholar

Bromiley, G.D., and Pawley, A.R. (2002) The high-pressure stability of Mg-sursassite in a model hydrous peridotite: A possible mechanism for the deep subduction of significant volumes of H2O. Contributions to Mineralogy and Petrology, 142, 714–723.10.1007/s00410-001-0318-5Search in Google Scholar

Bruker (2016) APEX3SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, U.S.A.Search in Google Scholar

Fockenberg, T. (1998) An experimental study of the pressure–temperature stability of MgMgAl-pumpellyite in the system MgO–Al2O3–SiO2–H2O. American Mineralogist, 83, 220–227.10.2138/am-1998-3-404Search in Google Scholar

Gottschalk, M., Fockenberg, T., Grevel, K.-D., Wunder, B., Wirth, R., Schreyer, W., and Maresch, W.V. (2000) Crystal structure of the high-pressure phase Mg4(MgAl) Al4[Si6O21(OH)7 an analogue of sursassite. European Journal of Mineralogy, 12, 935–945.10.1127/ejm/12/5/0935Search in Google Scholar

Hill, R.J., Newton, M.D., and Gibbs, G.V. (1983) A crystal chemical study of stishovite. Journal of Solid State Chemistry, 47, 185–200.10.1016/0022-4596(83)90007-5Search in Google Scholar

Irifune, T., Kurio, A., Sakamoto, S., Inoue, T., Sumiya. H., and Funakoshi, K. (2004) Formation of pure polycrystalline diamond by direct conversion of graphite at high pressure and high temperature. Physics of the Earth and Planetary Interiors, 143–144, 593–600.10.1016/j.pepi.2003.06.004Search in Google Scholar

Katsura, T., and Ito, E. (1989) The system Mg2SiO4-Fe2SiO4 at high pressure and temperatures: Precise determination of stabilities of olivine, modified spinel, and spinel. Journal of Geophysical Research, 94, 15663–15670.10.1029/JB094iB11p15663Search in Google Scholar

Nagashima, M., Rahmoun, N.S., Alekseev, E.V., Geiger, C.A., Armbruster, T., and Akasaka, M. (2008) Crystal chemistry of macfallite: Relationships to sursassite and pumpellyite. American Mineralogist, 93, 1851–1857.10.2138/am.2008.2935Search in Google Scholar

Nagashima, M., Akasaka, M., Minakawa, T., Libowitzky, E., and Armbruster, T. (2009) Sursassite: hydrogen bonding, cation order, and pumpellyite intergrowth. American Mineralogist, 94, 1440–1449.10.2138/am.2009.3223Search in Google Scholar

Plank, T., and Langmuir, C.H. (1998) The chemical composition of subducting sediment and its consequences for the crust and mantle. Chemical Geology, 145, 325–394.10.1016/S0009-2541(97)00150-2Search in Google Scholar

Schreyer, W. (1988) Experimental studies on metamorphism of crustal rocks under mantle pressures. Mineralogical Magazine, 52, 1–26.10.1180/minmag.1988.052.364.01Search in Google Scholar

Sheldrick, G.M. (2008) A short history of SHELX. Acta Crystallographica, A64, 112–122.10.1107/S0108767307043930Search in Google Scholar PubMed

Wilson, A.J.C., Ed. (1992) International Tables for Crystallography, Volume C: Mathematical, physical and chemical tables. Kluwer Academic.Search in Google Scholar

Received: 2020-03-31
Accepted: 2020-05-28
Published Online: 2020-09-20
Published in Print: 2020-09-25

© 2020 Walter de Gruyter GmbH, Berlin/Boston

Downloaded on 1.4.2023 from
Scroll to top button