Pressure-induced dehydration of dioptase: A single-crystal X-ray diffraction and Raman spectroscopy study |
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| Institution: | 1. Key Laboratory of Orogenic Belts and Crustal Evolution, MOE, Peking University and School of Earth and Space Sciences, Peking University, Beijing, China;2. Department of Earth and Planetary Sciences, Northwestern University, Evanston, IL, USA;3. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, China;4. School of Ocean and Earth Science and Technology, Hawai’i Institute of Geophysics and Planetology, University of Hawaii at Manoa, Honolulu, Hawaii, USA;5. Center for Advanced Radiation Sources, University of Chicago, Chicago, IL, USA |
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| Abstract: | We present a synchrotron-based, single-crystal X-ray diffraction and Raman spectroscopy study of natural green dioptase (Cu6Si6O18·6H2O) up to ～30 GPa at room temperature. The lattice parameters of dioptase exhibit continuous compression behavior up to ～14.5 GPa, whereupon a structural transition is observed. Pressure–volume data below 14.5 GPa were fitted to a second-order Birch–Murnaghan equation of state with V0 = 1440(2) Å3 and K0 = 107(2) GPa, with K0′ = 4(fixed). The low-pressure form of dioptase exhibits anisotropic compression with axial compressibility βa > βc in a ratio of 1.14:1.00. Based on the diffraction data and Raman spectroscopy, the new high-pressure phase could be regarded as a dehydrated form of dioptase in the same symmetry group. Pressure-induced dehydration of dioptase contributes broadly to our understanding of the high-pressure crystal chemistry of hydrous silicates containing molecular water groups. |
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| Keywords: | Dioptase Pressure-induced dehydration Synchrotron single-crystal X-ray diffraction Compressibility |
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