A multi-analytical study of the crystal structure of unusual Ti–Zr–Cr-rich Andradite from the Maronia skarn, Rhodope massif, western Thrace, Greece

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...

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Bibliographic Details
Published in:Mineralogy and petrology Vol. 95; no. 1-2; pp. 113 - 124
Main Authors: Katerinopoulou, A., Katerinopoulos, A., Voudouris, P., Bieniok, A., Musso, M., Amthauer, G.
Format: Journal Article
Language:English
Published: Vienna Springer Vienna 2009
Springer Nature B.V
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Summary: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.% TiO 2 , 8 wt.% Cr 2 O 3 and 4 wt.% ZrO 2 , representing a solid solution of andradite (Ca 3 Fe 3+ 2 Si 3 O 12 ≈46 mol%), uvarovite (Ca 3 Cr 2 Si 3 O 12 ≈23 mol%), grossular (Ca 3 Al 2 Si 3 O 12 ≈10 mol%), schorlomite (Ca 3 Ti 2 [Si,(Fe 3+ ,Al 3+ ) 2 ]O 12 ≈15 mol%), and kimzeyite (Ca 3 Zr 2 [Si,Al 2 ] 3 O 12 ≈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 Al 3+ , Fe 3+ and Ti 4+ . Cr 3+ and Zr 4+ are found at the octahedral site along with Fe 3+ , Al 3+ and Ti 4+ . The measured H 2 O content is 0.20 wt.%. The analytical data suggest that the structural formula of the Maronia garnet can be given as: (Ca 2.99 Mg 0.03 ) Σ=3.02 (Fe 3+ 0.67 Cr 0.54 Al 0.33 Ti 0.29 Zr 0.15 ) Σ=1.98 (Si 2.42 Ti 0.24 Fe 0.18 Al 0.14 ) Σ=2.98 O 12 OH 0.11 . 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.
ISSN:0930-0708
1438-1168
DOI:10.1007/s00710-008-0023-4