Raman spectroscopic characterization of K-cymrite (KAlSi₃O₈*H₂O) and its anhydrous phase (kokchetavite)

Abstract

To help identification of K-cymrite (KAlSi3O8*H2O) and its anhydrous form (kokchetavite) in UHP metamorphic rocks, K-cymrite and kokchetavite are studied by Raman spectroscopy. K-cymrite is produced at 5 GPa and 800 C. Kokchetavite is made by dehydration of K-cymrite heating up to 800 C. In-situ high pressure Raman spectra of two phases are obtained using diamond anvil cell. Raman shifts of the main peak for K-cymrite and kokchetavite are 380 and 390 cm-1, respectively. Our result reveals that the previously reported K-cymrite from China (Zhang et al., AM, 2008) would be kokchetavite rather than K-cymrite. Pressure dependences of Raman shifts for main peaks for K-cymrite and kokchetavite are 4.9 and 5.6 cm-1/GPa, respectively.