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Mineralogical ClassificationCrystal structures of synthetic sekaninaite and ferroindialite
29th Jul 2014 13:40 UTCUwe Kolitsch Manager
The crystal structures of synthetic hexagonal and orthorhombic Fe-cordierite polymorphs with the space groups P6/mcc and Cccm were refined from single-crystal X-ray diffraction data to R 1, hex = 3.14 % and R 1, ortho = 4.48 %. The substitution of the larger Fe2+ for Mg leads to multiple structural changes and an increase of the unit cell volumes, with a, c (hex) = 9.8801(16) Å, 9.2852(5) Å and a, b, c (ortho) = 17.2306(2) Å, 9.8239(1) Å, 9.2892(1) Å in the end-members. Furthermore Fe incorporation results in an increase of the volumes of the octahedra, although the diameters of the octahedra in direction of the c-axis decrease in both polymorphs. X-ray powder diffraction analysis indicates a high degree of Al/Si ordering in the orthorhombic polymorph, the Miyashiro distortion index is ~0.24. Estimations of site occupancies based on the determined tetrahedral volumes result in the following values for hexagonal Fe-cordierite: ~73 % Al for T1 and ~28 % Al for T2. For the first time Raman spectroscopy was performed on the hexagonal Fe-cordierite polymorph. In the hexagonal Fe-cordierite polymorph most Raman peaks are shifted towards lower wavenumbers when compared with the Mg-end-member.
29th Aug 2014 16:16 UTCKnut Edvard Larsen 🌟 Manager
Chukanov, N.V., Aksenov, S.M., Pekov, I.V., Ternes, В., Schüller, W., Belakovskiy, D.I., Van, K.V., Blass, G. (2014): Ferroindialite (Fe2+,Mg)2Al4Si5O18, a new beryl-group mineral from the Eifel volcanic region, Germany. Zapiski RMO, 143, 46-56.
See abstract here: http://www.minsoc.ru/FilesBase/2143103e.pdf
Data added to mineralpage
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