Systematic measurement of the intrinsic losses in various kinds of bulk   fused silica
  We systematically measured and compared the mechanical losses of various kinds of bulk fused silica. Their quality factors ranged widely from 7x10^5 to 4x10^7, the latter being one of the highest reported among bulk fused silica. We observed frequency-dependent losses and a decrease in the losses upon annealing. 
K. Numata, K. Yamamoto, H. Ishimoto, S. Otsuka, K. Kawabe, M. Ando,   and K. Tsubono