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A. Katerinopoulou A. Katerinopoulos P. Voudouris A. Bieniok M. Musso G. Amthauer 《Mineralogy and Petrology》2009,95(1-2):113-124
Unusual Ti–Cr–Zr-rich garnet crystals from high-temperature melilitic skarn of the Maronia area, western Thrace, Greece, were investigated by electron-microprobe analysis, powder and single-crystal X-ray diffraction, IR, Raman and Mössbauer spectroscopy. Chemical data showed that the garnets contain up to 8 wt.% TiO2, 8 wt.% Cr2O3 and 4 wt.% ZrO2, representing a solid solution of andradite (Ca3Fe3+ 2Si3O12 ≈46 mol%), uvarovite (Ca3Cr2Si3O12 ≈23 mol%), grossular (Ca3Al2Si3O12 ≈10 mol%), schorlomite (Ca3Ti2[Si,(Fe3+,Al3+)2]O12 ≈15 mol%), and kimzeyite (Ca3Zr2[Si,Al2]3O12 ≈6 mol%). The Mössbauer analysis showed that the total Fe is ferric, preferentially located at the octahedral site and to a smaller extent at the tetrahedral site. Single-crystal XRD analysis, Raman and IR spectroscopy verified substitution of Si mainly by Al3+, Fe3+ and Ti4+. Cr3+ and Zr4+ are found at the octahedral site along with Fe3+, Al3+ and Ti4+. The measured H2O content is 0.20 wt.%. The analytical data suggest that the structural formula of the Maronia garnet can be given as: (Ca2.99Mg0.03)Σ=3.02(Fe3+ 0.67Cr0.54Al0.33Ti0.29Zr0.15)Σ=1.98(Si2.42Ti0.24Fe0.18Al0.14)Σ=2.98O12OH0.11. Ti-rich garnets are not common and their crystal chemistry is still under investigation. The present work presents new evidence that will enable the elucidation of the structural chemistry of Ti- and Cr-rich garnets. 相似文献
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Zucchini A. Comodi P. Katerinopoulou A. Balic-Zunic T. McCammon C. Frondini F. 《Physics and Chemistry of Minerals》2012,39(4):319-328
A combined powder and single-crystal X-ray diffraction analysis of dolomite [CaMg(CO3)2] heated to 1,200°C at 3 GPa was made to study the order–disorder–reorder process. The order/disorder transition is inferred
to start below 1,100°C, and complete disorder is attained at approximately 1,200°C. Twinned crystals characterized by high
internal order were found in samples annealed over 1,100°C, and their fraction was found to increase with temperature. Evidences
of twinning domains combined with probable remaining disordered portions of the structure imply that reordering processes
occur during the quench. Twin domains are hereby proposed as a witness to thermally induced intra-layer-type cation disordering. 相似文献
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A. Katerinopoulou A. Katerinopoulos A. Bieniok E. Knop A. Magganas G. Amthauer 《Mineralogy and Petrology》2007,91(1-2):117-128
Summary Pyroxene samples, from the Greek island of Syros, taken from a blueschist-eclogite facies Mg-rich metagabbro, were investigated
by chemical and XRD analyses and M?ssbauer spectroscopy.
Single-crystal XRD and microprobe analysis showed that the natural sample is a typical omphacite of intermediate composition
in the Ca–Na pyroxene solid solutions. The space group P2/n was confirmed and the cations Mg, Al and Ca, Na were found to be ordered in the M1 and M2 positions, respectively. M?ssbauer
spectroscopy showed that there is both ferrous and ferric iron in the structure, with the ratio 1.38:1. The M2 sites are fully
occupied by Ca and Na, thus the iron (Fe2+ and Fe3+) can substitute only for Mg and Al in the M1 sites.
Partial disorder was attained by annealing the sample at 850 °C, 20 kbar for 7 days, as confirmed by decrease of intensity
of reflections affected by the C-type extinction. 相似文献
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