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Non-ideality and defectivity of the åkermanite-gehlenite solid solution: An X-ray diffraction and TEM study

  • Mauro Gemmi EMAIL logo , Marco Merlini , Giuseppe Cruciani and Gilberto Artioli
Published/Copyright: April 1, 2015
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American Mineralogist
From the journal American Mineralogist Volume 92 Issue 10

Abstract

This paper reports a structure analysis of the åkermanite-gehlenite solid solution. This solution is non-ideal with a negative excess volume in the entire compositional range. X-ray diffraction shows anomalous behavior of the cell parameters close to the gehlenite end-member (åk08ge92, åk35ge65). This behavior is correlated with an excess of Si and deficiency of Al with respect to the Mg content, which implies a defective, non-stoichiometric structure with Ca vacancies. Electron microscopy images have confirmed an increase in the defectivity on the atomic scale for Al-rich compositions, and single-crystal structure refinements show a correlated decrease of the tetrahedral volume preferentially occupied by Si. The incommensurate modulation, characteristic of åkermanite, has been observed also in åk95ge05, and it is still visible as diffuse scattering in åk75ge25. (210) twinning has been observed in the entire compositional range.

Keywords: Melilite; solid solution; X-ray diffraction; electron microscopy
Received: 2006-7-6
Accepted: 2007-5-31
Published Online: 2015-4-1
Published in Print: 2007-10-1

© 2015 by Walter de Gruyter Berlin/Boston

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https://doi.org/10.2138/am.2007.2380
Keywords for this article
Melilite; solid solution; X-ray diffraction; electron microscopy

Articles in the same Issue

  1. Ferric iron in Al-bearing akimotoite coexisting with iron-nickel metal in a shock-melt vein in an L-6 chondrite
  2. Solidification and microstructures of binary ice-I/hydrate eutectic aggregates
  3. A monazite oxygen isotope thermometer
  4. The albite fusion curve re-examined: New experiments and the high-pressure density and compressibility of high albite and NaAlSi3O8 liquid
  5. XRD and HRTEM analyses of stacking structures in sudoite, di-trioctahedral chlorite
  6. Vibrational dynamics in H+-substituted forsterite: A first-principles molecular dynamics study
  7. Fluorophlogopite from Biancavilla (Mt. Etna, Sicily, Italy): Crystal structure and crystal chemistry of a new F-dominant analog of phlogopite
  8. Pressure-induced over-hydration of thomsonite: A synchrotron powder diffraction study
  9. High-pressure optical spectroscopy and X-ray diffraction studies on synthetic cobalt aluminum silicate garnet
  10. In situ observation of the decomposition of kyanite at high pressures and high temperatures
  11. Mineralogy and crystal structure of bouazzerite from Bou Azzer, Anti-Atlas, Morocco: Bi-As-Fe nanoclusters containing Fe3+ in trigonal prismatic coordination
  12. Single-crystal structure refinement of diaspore at 50 GPa
  13. FTIR spectroscopy of Ti-rich pargasites from Lherz and the detection of O2- at the anionic O3 site in amphiboles
  14. The relative stability of monazite and huttonite at 300 - 900 °C and 200 - 1000 MPa: Metasomatism and the propagation of metastable mineral phases
  15. Acoustic dissipation associated with phase transitions in lawsonite, CaAl2Si2O7(OH)2·H2O
  16. Magnetic anisotropy of carbonate minerals at room temperature and 77 K
  17. Non-ideality and defectivity of the åkermanite-gehlenite solid solution: An X-ray diffraction and TEM study
  18. The system Al2O3-P2O5-H2O at temperatures below 200 °C: Experimental data on the stability of variscite and metavariscite AlPO4·2H2O
  19. Low-pressure decomposition of chrysotile as a function of time and temperature
  20. Ion exchange equilibrium and structural changes in clinoptilolite irradiated with β- and γ-radiation: Monovalent cations
  21. Investigation of dioctahedral smectite hydration properties by modeling of X-ray diffraction profiles: Influence of layer charge and charge location
  22. Growth of large (1 mm) MgSiO3 perovskite single crystals: A thermal gradient method at ultrahigh pressure
  23. Carbon is not required during crystallization to produce ferrobasalts/ferrodiorites (FTP rocks)
  24. Letter: Meridianiite: A new mineral species observed on Earth and predicted to exist on Mars
  25. Letter: Equations of state of CaIrO3 perovskite and post-perovskite phases
  26. Letter: Hydrogen-carbonate ion in synthetic high-pressure apatite
  27. Letter: Effects of irradiation damage on the back-scattering of electrons: Silicon-implanted silicon
  28. Letter: High-precision oxygen isotope analysis of picogram samples reveals 2 μm gradients and slow diffusion in zircon
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