5:15 PM - 6:30 PM
[SCG57-P08] Elastic constants of single-crystal topaz and their temperature dependence studied via sphere-resonance method
Keywords:elastic constants, resonance method, hydrous mineral, topaz
A sphere sample (D=6.483(1) mm) was made from a topaz single-crystal (Al1.97SiO4(F1.56,OH0.42)) collected from Nakatsugawa, Gifu Pref. by the two-pipe method. The uniformity of crystallographic orientation was confirmed with SEM-EBSD (Shizuoka Univ.) measurement. Resonant frequencies were measured at frequencies from 600 kHz to 1.5 MHz with different specimen-holding forces. Extrapolating to the specimen-holding force of zero, we obtained frequencies of "free" oscillation. The temperature was changed from 0 to 40ºC. Elastic constants were determined by comparing measured and calculated resonant frequencies. The xyz algorithm (Visscher et al., 1991) was employed to calculate resonant frequencies of the sphere sample. At room temperature (18.7ºC), C11=281.3, C22=346.3, C33=294.8, C44=108.5, C55=132.5, C66=130.3, C12=121.5, C13=80.90, C23=81.73 (GPa). Using determined elastic constants, compressional- and shear-wave velocities were estimated for an isotropic polycrystalline aggregate of topaz at high temperature. Compresional- and shear-wave velocities at 800ºC are 9.32 km/s and 5.57 km/s, respectively. These values are significantly higher than those in minerals like olivine or garnet.