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.
- Pressure-induced dehydration
- Synchrotron single-crystal X-ray diffraction
ASJC Scopus subject areas
- Global and Planetary Change
- Earth and Planetary Sciences(all)