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Raman and NMR spectroscopic characterization of high-pressure K-cymrite (KAlSi3O8.H2O) and its anhydrous form (kokchetavite)

Abstract : To facilitate identification of high-pressure K-cymrite (KAlSi3O8·H2O) phase and its anhydrous form (kokchetavite) in natural rocks, we have synthesized both phases and have characterized them by micro-Raman and NMR spectroscopy. K-cymrite was synthesized at 5 GPa and 800 °C. Kokchetavite was obtained by dehydrating K-cymrite at ambient pressure and 550 °C. The 1H MAS and 1H-29Si CP MAS NMR spectra of K-cymrite are consistent with the reported crystal structure that contains H2O molecules and has a disordered Si-Al distribution. The Raman spectra obtained under ambient conditions for K-cymrite (and kokchetavite) contain major peaks at 114.0 (109.1), 380.2 (390.0) and 832.5 (835.8) cm-1. For K-cymrite, OH stretching vibration is also observed at 3541 cm-1 with a shoulder at 3623 cm-1. The Raman spectrum for kokchetavite is consistent with that previously reported for a natural sample found as inclusions in clinopyroxenes and garnets in a garnet-pyroxene rock. However, the data for K-cymrite are inconsistent with the Raman features of a previously reported “relict K-cymrite in K-feldspar” from an eclogite. Pressure- and temperature-dependencies of the Raman shifts for the strongest peak of both phases are also reported.
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Submitted on : Monday, February 21, 2022 - 5:16:29 PM
Last modification on : Wednesday, February 23, 2022 - 3:34:59 AM

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Masami Kanzaki, Xianyu Xue, Julien Amalberti, Qian Zhang. Raman and NMR spectroscopic characterization of high-pressure K-cymrite (KAlSi3O8.H2O) and its anhydrous form (kokchetavite). Journal of Mineralogical and Petrological Sciences, 2012, 107, pp.114-119. ⟨10.2465/jmps.111020i⟩. ⟨insu-03583379⟩

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