Variation of Raman Spectra of Oligoclase under 1. 0∼4. 4 GPa

Variation of crystal structure of oligoclase with pressure was investigated by the approach of diamond anvil cell (DAC) and in situ micro-Raman spectroscopic measurement at room temperature and under pressures from 1. 0 to 4. 4 GPa. At 2. 9 GPa a new peak round 517 cm(-1) appeared, and a new phase was produced. Near 3. 4 GPa a major discontinuity occurs in the pressure dependence of 288 cm(-1) peak arising from the stretching mode of M-O, and 517 cm(-1) peak disappeared, it implied that the oligoclase underwent triclinic to monoclinic phase transition completely at about 3. 4 GPa. The peaks at 458 and 516 cm(-1) peaks arising from flexural vibrational mode of Si-O-Si shifted linearly with the increasing pressures, the pressure-related slopes are 1. 667 cm(-1)/GPa and 3. 560 cm(-1)/GPa, respectively, whereas, the flexural vibrational mode of Al-O-Al at 480 cm(-1) did not shifted linearly with the increasing pressures. The position of 288 cm(-1) peak did not change obviously in comparision with 458, 516 and 480 cm(-1) peaks, which shifted to lower frequency during decompression. The phase transition pressure of feldspar relates to the species of cation in the octatomic rings.